Food Science & Technology · Product, Health & Industry · also Food Industry Waste Management, By-product Utilisation, Sustainable Food Processing, Environmental Management in Food Industry
Reducing and using food-industry waste: characterisation and treatment of food-plant effluents, recovery of by-products, water and energy reduction, life-cycle assessment and circular-economy approaches. General agricultural waste engineering is in Agricultural Engineering's waste-management-environmental-engg.
In the exams: GATE XE-G Section 3 (waste utilisation); ICAR AIEEA-PG Code 18 Unit III (effluent treatment, waste solids upgrading); ICAR AICE 41 (waste disposal of food processing plants)
A food factory takes in raw materials, water and energy and sends out not only products but also peels, bran, whey, blood, shells, wastewater, steam, carbon dioxide and spoiled or surplus food. Much of what leaves as waste still contains protein, fibre, sugars, oils and bioactive compounds, and all of it has an environmental cost. Reducing that waste, recovering value from it and treating what remains is now a central part of food technology: it lowers costs, meets environmental law, answers the demands of customers and investors, and contributes to the international goal of halving food waste and reducing food loss.
This subject covers food loss and waste along the supply chain and how they are measured; the characteristics of food-industry wastes, expressed as BOD, COD and solids; the primary, secondary and tertiary treatment of food-plant effluents; anaerobic digestion of food-processing waste to biogas; recovery of by-products from fruit, cereal, dairy, meat and fish processing; extraction of bioactive compounds from by-products; water reuse and the water footprint of food plants; energy efficiency and carbon footprint; life-cycle assessment of food products; circular-economy approaches and upcycled foods; and the environmental regulation that food industries must meet. General agricultural waste engineering is taught in Agricultural Engineering's waste-management-environmental-engg, and plant utilities in food-plant-design-utilities.
The subject is examined in graduate entrance examinations in food technology, which include waste utilisation such as pectin from fruit waste and the use of rice-milling by-products; in postgraduate examinations, which ask about effluent treatment and upgrading of waste solids; in research-fellowship examinations in processing and food engineering, which include waste disposal of food-processing plants; and in national technical qualifications. The practice questions follow those patterns and include the standard calculations of BOD, organic loads, biogas yields, water and carbon footprints.
FAO distinguishes food loss from food waste. Food loss is the decrease in the quantity or quality of food resulting from decisions and actions by food suppliers in the chain, from harvest up to, but excluding, retail; food waste is the decrease resulting from decisions and actions by retailers, food services and consumers. The distinction matters because causes and solutions differ. Sustainable Development Goal target 12.3 calls for halving per capita global food waste at the retail and consumer levels and reducing food losses along production and supply chains, including post-harvest losses, by 2030. FAO's Food Loss Index has estimated that about 13 to 14 per cent of food produced is lost between harvest and retail, and UNEP's Food Waste Index reports have estimated that about a sixth to a fifth of the food available to consumers is wasted in households, food service and retail, with households the largest share. Food loss and waste together have been estimated to account for roughly 8 to 10 per cent of global greenhouse gas emissions, in addition to the land, water, fertiliser and labour used to produce food that is not eaten.
Causes vary by stage and region. In primary production and post-harvest handling, losses arise from pests, diseases, poor harvesting practice, lack of drying and storage, absence of cold chains and poor roads, and are proportionally larger in many low-income countries for perishable fruit, vegetables, fish and milk and for grains in humid climates. In processing, losses come from trimming, peeling, rejected product, process faults, overproduction and line changeovers. In distribution and retail, they come from damage, cosmetic standards that reject misshapen produce, overstocking and short shelf life. In food service and households, which dominate waste in many middle- and high-income countries, they come from overbuying, large portions, poor storage, confusion over date labels and leftovers that are not eaten.
The food waste hierarchy ranks options by environmental and social value. Prevention at source is best, through better forecasting, process control, packaging, shelf-life extension and consumer behaviour. Next is redistribution of safe surplus food to people, through food banks and charities. Then use as animal feed, where safe and lawful. Then valorisation into ingredients, materials, chemicals or fuels. Then recovery of nutrients and energy by anaerobic digestion and composting. Then incineration with energy recovery. Disposal by landfill is the least preferred, because food decomposing in landfills produces methane, a potent greenhouse gas. The hierarchy is a guide, not a rule; life-cycle assessment may show that a lower option is better in a particular case.
Measuring food loss and waste is the basis of reducing it. The Food Loss and Waste Accounting and Reporting Standard, published in 2016 by a partnership of international organisations, sets out how a country, city or company defines the scope of its inventory (which materials, which stages, which destinations), how it quantifies the amounts (direct weighing, waste composition analysis, records, mass balance, modelling) and how it reports them. It distinguishes edible food from associated inedible parts such as bones, peels and shells, which matter for the hierarchy because inedible parts cannot be prevented in the same way. In a food factory, a mass balance of inputs and outputs, with each waste stream weighed and characterised, identifies the largest losses and their causes; targets, monitoring and a named owner for each stream turn the data into reductions. Many companies now report food loss and waste publicly, alongside water and carbon, and join collaborative agreements to meet the SDG target.
Food-industry wastewaters are mainly organic: sugars, starches, proteins, fats and organic acids dissolved or suspended in water from washing, cleaning, cooling, blanching, and product losses. Their main environmental effect is that, discharged to a river or lake, bacteria consume dissolved oxygen as they degrade the organic matter, which kills fish and other aquatic life. The strength of a wastewater is therefore expressed as its oxygen demand.
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen consumed by microorganisms degrading the organic matter in a sample, conventionally measured over 5 days at 20 °C in the dark (BOD₅). A sample is diluted with aerated, seeded dilution water, the dissolved oxygen is measured at the start (D₁) and after 5 days (D₂), and BOD₅ = (D₁ − D₂)/P, where P is the decimal fraction of sample in the bottle. For example, if a dairy effluent is diluted 1 in 100 (P = 0.01) and dissolved oxygen falls from 8.5 to 4.0 mg/L, the BOD₅ is 450 mg/L. Chemical oxygen demand (COD) is the amount of oxygen equivalent to the organic matter oxidised by a strong chemical oxidant, potassium dichromate in hot sulphuric acid, in about two hours; it is faster and more reproducible than BOD and includes compounds that microbes degrade slowly or not at all, so COD is always greater than or equal to BOD. The BOD/COD ratio indicates biodegradability: values above about 0.5 suggest readily biodegradable wastewater, typical of many food effluents, while low ratios suggest refractory or toxic components. Total organic carbon (TOC), measured by combustion, is a third measure.
Solids are measured in several fractions. Total solids are the residue after evaporation; total suspended solids (TSS) are retained on a filter of standard pore size and dried at 103 to 105 °C; total dissolved solids pass through the filter; and volatile solids are the part lost on ignition at 550 °C, an approximate measure of organic matter. Settleable solids, measured in an Imhoff cone, indicate how much will settle in a primary clarifier. Fats, oils and grease (FOG) are measured by solvent extraction; they float, coat pipes and clog sewers and treatment plants, and are high in meat, dairy, edible-oil and frying effluents. Nutrients, nitrogen (as total Kjeldahl nitrogen, ammonia and nitrate) and phosphorus (from proteins, phosphate detergents and some products), cause eutrophication of receiving waters. Other parameters are pH (cleaning chemicals swing it from very acid to very alkaline), temperature, salinity (from brines, pickling and cheese making), colour and specific pollutants such as residual sanitisers.
Treatment design and charges depend on loads, not only concentrations. The organic load in kilograms per day is the concentration in mg/L multiplied by the flow in m³/day and divided by 1000; for example, 500 m³/day at a BOD of 2000 mg/L is 1000 kg BOD per day. Loads are often compared with the population equivalent, the load produced by one person, which European rules define as 60 g of BOD₅ per day; the effluent in this example equals about 16 700 population equivalents, the sewage of a small town. Food effluents vary greatly in strength: dairy, brewery, distillery, starch, sugar, fruit and vegetable, meat and fish plants typically produce wastewaters with BOD from hundreds to many thousands of mg/L, with daily and seasonal variations linked to production and cleaning, which is why equalisation tanks and monitoring of flows and concentrations are part of plant design. Solid wastes, such as peels, trimmings, sludges and spent materials, are characterised by moisture, organic content, nutrient content and potential contaminants to decide their best use.
Food-plant effluents are treated on site before discharge to a river or sea, or pre-treated before discharge to a municipal sewer, depending on the permit. Treatment is described in stages. Preliminary treatment removes material that would damage or block later stages: coarse and fine screens (rotary drum and wedge-wire screens) remove peels, fibres and particles, often recovering them for feed or digestion; grit chambers remove sand from vegetable washing; and fat traps or grease interceptors hold back floating fat. Because flows and strengths fluctuate with production and cleaning, an equalisation (balancing) tank evens out flow, concentration, temperature and pH before biological treatment, and neutralisation with acid or alkali brings the pH into a range suitable for microbes, typically about 6.5 to 8.5. Mixing acidic and alkaline cleaning wastes in the balancing tank is a useful form of self-neutralisation.
Primary treatment removes suspended solids and FOG by physical and physico-chemical means. Gravity sedimentation in clarifiers settles heavier particles. Dissolved air flotation (DAF) is widely used in meat, poultry, dairy, fish and edible-oil plants: water saturated with air under pressure is released into the tank, forming fine bubbles that attach to fat and particles and float them to the surface, where they are skimmed off; coagulants (such as aluminium or iron salts) and polymer flocculants are added to improve removal, and the DAF sludge, rich in fat and protein, can be rendered or digested. Primary treatment typically removes a large share of TSS and FOG and part of the BOD, reducing the load on biological treatment.
Secondary treatment removes dissolved and colloidal organic matter biologically. In aerobic processes, bacteria oxidise organic matter to carbon dioxide and water and grow new biomass. The activated-sludge process mixes wastewater with a suspension of microorganisms (mixed liquor) in an aerated tank and then separates the sludge in a clarifier, returning most to the tank and wasting the excess. Design and control use the hydraulic retention time (HRT = V/Q, the tank volume divided by the flow), the solids retention time or sludge age, the mixed-liquor suspended solids, and the food-to-microorganism ratio, F/M = (Q × S₀)/(V × X), where S₀ is the influent BOD and X the biomass concentration; for example, 1000 m³/day at 1500 mg/L BOD into a 3000 m³ tank with 3000 mg/L MLSS gives F/M ≈ 0.17 kg BOD per kg MLSS per day. Variants include sequencing batch reactors, which carry out all steps in one tank in timed cycles; membrane bioreactors, which replace the clarifier with membranes, giving high-quality effluent suitable for reuse; trickling filters and rotating biological contactors with fixed biofilms; moving-bed biofilm reactors; and aerated lagoons and stabilisation ponds where land is available. Strong effluents are often treated first anaerobically (chapter 4), which removes most of the COD with little energy, and then aerobically to meet discharge limits. Sludge from biological treatment is thickened, dewatered (belt presses, centrifuges) and digested, composted, applied to land where permitted, or incinerated.
Tertiary treatment polishes the effluent to stricter limits or for reuse. Biological nitrogen removal combines nitrification (ammonia to nitrate by autotrophic bacteria under aerobic conditions) and denitrification (nitrate to nitrogen gas by heterotrophs under anoxic conditions, using organic carbon). Phosphorus is removed by chemical precipitation with iron or aluminium salts or by enhanced biological phosphorus removal. Filtration through sand or membranes removes remaining suspended solids, activated carbon removes colour and trace organics, and disinfection by ultraviolet light, chlorination or ozonation reduces pathogens. Reverse osmosis can produce water of high quality for reuse in boilers, cooling or, with regulatory approval, cleaning. Discharge limits are set in each plant's permit by the regulator, according to the receiving water and national standards, and are typically expressed for BOD, COD, TSS, FOG, nutrients and pH.
Anaerobic digestion converts organic matter, in the absence of oxygen, into biogas, a mixture of methane (typically about 50 to 70 per cent) and carbon dioxide with traces of hydrogen sulphide and water vapour, and a digestate. It is carried out by a consortium of microorganisms in four stages. In hydrolysis, extracellular enzymes break polymers (carbohydrates, proteins and fats) into sugars, amino acids and fatty acids; for solid and fatty wastes this is often the rate-limiting step. In acidogenesis, fermentative bacteria convert these into volatile fatty acids (acetic, propionic, butyric), alcohols, hydrogen and carbon dioxide. In acetogenesis, syntrophic bacteria convert propionate, butyrate and alcohols into acetate, hydrogen and carbon dioxide, a step that is thermodynamically possible only when hydrogen-consuming methanogens keep the hydrogen partial pressure very low. In methanogenesis, methanogenic archaea produce methane: acetoclastic methanogens split acetate into methane and carbon dioxide, producing most of the methane in typical digesters, and hydrogenotrophic methanogens combine hydrogen and carbon dioxide.
Methanogens are slow-growing and sensitive, so digester conditions are controlled. Temperature is held either in the mesophilic range (about 35 to 37 °C) or the thermophilic range (about 50 to 55 °C), which gives faster digestion and better pathogen reduction but is less stable. The pH is kept near neutral, about 6.8 to 7.4, with enough alkalinity to buffer the volatile fatty acids; a rise in the ratio of volatile acids to alkalinity is an early warning of failure. A carbon-to-nitrogen ratio of about 20 to 30 suits the microbes; too much nitrogen, as in protein-rich slaughterhouse waste, raises free ammonia, which inhibits methanogens, while too little limits growth. Other inhibitors are long-chain fatty acids from fat overload, hydrogen sulphide from sulphate-rich wastes, salts, disinfectants and antibiotics. Overloading a digester with readily degradable sugars produces acids faster than methanogens can consume them, so the pH falls and the digester 'sours'.
Digesters for food wastes are of several types. Completely mixed tank digesters handle slurries and solid wastes such as fruit and vegetable residues, food waste and manure. High-rate reactors retain biomass independently of the liquid flow and treat strong wastewaters in compact tanks: the upflow anaerobic sludge blanket (UASB) reactor, in which wastewater flows upwards through a blanket of dense granules of microorganisms, with a gas-solid-liquid separator at the top, is widely used for brewery, distillery, starch, sugar, potato, dairy and soft-drink effluents; expanded granular sludge bed and internal circulation reactors are higher-rate developments; anaerobic filters hold biomass on packing. Covered anaerobic lagoons are used where land is cheap.
The theoretical methane yield follows from the oxygen equivalence of methane: each kilogram of COD converted to methane gives about 0.35 m³ of methane at standard temperature and pressure (0 °C, 1 atm), or about 0.40 m³ at 35 °C. Methane has a lower heating value of about 35.8 MJ per m³ at standard conditions, roughly 10 kWh. For example, a UASB treating 2000 kg COD per day with 85 per cent removal, of which most is converted to methane, can yield up to about 0.85 × 2000 × 0.35 = 595 m³ of methane per day, about 21 GJ, less the small fraction of COD that becomes sludge or leaves dissolved. Biogas is burned in boilers to raise steam for the factory, used in combined heat and power engines (with electrical efficiencies of roughly 35 to 40 per cent and useful heat recovered), or upgraded to biomethane by removing carbon dioxide and hydrogen sulphide for injection into gas grids or use as vehicle fuel. Hydrogen sulphide must be removed because it corrodes engines and is toxic. The digestate, rich in nitrogen, phosphorus and potassium, is used as fertiliser where its quality and the law allow, after separation into liquid and fibre fractions. Anaerobic digestion therefore combines waste treatment, renewable energy and nutrient recycling; its economics depend on waste strength, gas use, energy prices, gate fees and incentives.
Processing removes large fractions of many raw materials: peels, seeds, pomace and cores can be a third to a half of the weight of some fruits. Citrus peel and apple pomace are the main commercial sources of pectin, which is extracted with hot dilute acid, separated, precipitated with alcohol, washed and dried; the degree of esterification is then adjusted to give high- or low-methoxyl pectins. Citrus peel also yields essential oil, chiefly d-limonene, recovered by cold pressing or steam distillation, and dried peel and pulp are used as cattle feed. Grape pomace from winemaking gives grape-seed oil, polyphenols, tartaric acid and spirits; tomato pomace gives lycopene and seed oil; mango kernels give a fat used in confectionery; and many fruit and vegetable residues are dried and milled into dietary fibre ingredients.
Cereal milling and processing produce bran, germ and husk. Rice bran, about a tenth of paddy by weight in some estimates, contains oil, protein, fibre and tocopherols and oryzanol, but its lipase rapidly releases free fatty acids after milling, so bran must be stabilised by heat (extrusion or dry heating) within hours if it is to be used for oil or food. Rice husk is burned as fuel, and its ash, rich in silica, has industrial uses. Wheat bran and germ are used in food and feed; maize wet milling gives germ oil, gluten feed and corn steep liquor, a nutrient for fermentation. Brewers' spent grain, the largest by-product of brewing, is used mainly as cattle feed and increasingly dried for flour and protein ingredients. Sugar manufacture gives bagasse (burned in mill boilers to generate steam and electricity, often exporting power to the grid), molasses (for fermentation to ethanol, yeast, citric acid and feed) and filter mud (used as soil amendment).
Whey, the liquid left after cheese or casein manufacture, is produced in volumes several times greater than the cheese itself and has a high BOD, so discharging it untreated is a serious pollutant and a waste of nutrients. Modern dairies process whey by ultrafiltration into whey protein concentrates and isolates, valued in sports, infant and clinical nutrition and as functional ingredients; the lactose-rich permeate is crystallised into lactose, dried as permeate powder, fermented into ethanol, or converted to galacto-oligosaccharides and other derivatives. Demineralised whey powders go into infant formula. Buttermilk from butter making is dried for use in bakery and confectionery.
Slaughter and meat processing produce blood, bones, skins, fat, offal and inedible material. Blood is processed into plasma proteins and haem iron for food or feed, or into blood meal. Bones and hides yield gelatin and collagen; fat is rendered into edible tallow and lard or industrial fats; and inedible material is rendered into meat and bone meal and fat. After the bovine spongiform encephalopathy epidemic, many countries banned or restricted the feeding of processed animal proteins to farmed animals, especially ruminants, and introduced risk-based categories for animal by-products that determine how each must be handled, from incineration of the highest-risk material to use of low-risk material in pet food and feed. Fish processing leaves heads, frames, viscera, skins and shells, which can be half of the raw weight. They are traditionally converted into fish meal and fish oil for aquaculture and animal feed, and a substantial share of world fish meal now comes from by-products rather than whole fish. Higher-value uses include fish protein hydrolysates made with enzymes, collagen and gelatin from skins, fish oil concentrates rich in long-chain omega-3 fatty acids, and chitin and chitosan from shrimp and crab shells, obtained by demineralisation with acid and deproteinisation with alkali, followed by deacetylation of chitin to chitosan. Fish silage, made by acidifying minced fish waste, is a simple method for small-scale operations. Each use requires attention to safety: freshness, microbial control and contaminants such as heavy metals and dioxins, which can concentrate in by-products.
Many by-products are rich in compounds with nutritional or technological value, often more concentrated than in the edible part: polyphenols in grape pomace, apple pomace, onion skins, olive-mill wastewater and coffee by-products; carotenoids such as lycopene in tomato peel and β-carotene in carrot pomace; dietary fibres and pectins in fruit and cereal residues; peptides from protein hydrolysates of whey, fish and meat by-products; and oils with tocopherols, phytosterols and specific fatty acids from seeds and bran. Olive-mill wastewater, for example, is both a pollutant and a source of hydroxytyrosol, a potent phenolic antioxidant. Recovering these compounds can turn a disposal cost into a revenue, but only if extraction, purification and stabilisation are economic and the product is safe and approved for its intended use.
Conventional methods include maceration or stirring in a solvent, Soxhlet extraction, and hydrodistillation for volatile oils. The solvent is chosen by polarity: water and ethanol-water mixtures for polyphenols and other polar compounds, hexane or ethyl acetate for oils and carotenoids. Extraction efficiency depends on particle size, solvent-to-solid ratio, temperature, time and the number of stages; heat and long times increase yield but can degrade sensitive compounds. Food-grade extraction prefers solvents permitted in food processing, such as water, ethanol, carbon dioxide and, within limits, hexane and some others, with residues controlled.
Newer techniques aim to increase yield and selectivity while using less solvent, energy and time. Ultrasound-assisted extraction uses acoustic cavitation, the formation and violent collapse of bubbles, to disrupt cell walls and increase mass transfer. Microwave-assisted extraction heats the water inside plant cells rapidly, rupturing them. Pressurised liquid extraction uses solvents above their boiling points under pressure to increase solubility and diffusion. Subcritical water extraction uses hot water (about 100 to 374 °C) kept liquid under pressure; as temperature rises, its polarity falls, so it can extract less polar compounds. Supercritical fluid extraction most commonly uses carbon dioxide above its critical point (31.1 °C and 7.38 MPa), where it has liquid-like density and gas-like diffusivity; it is non-toxic, leaves no residue and is easily removed by depressurisation, and its solvating power is tuned by pressure and temperature. Because supercritical CO₂ is non-polar, it suits oils, carotenoids and essential oils, and a polar co-solvent such as ethanol is added for polyphenols. Enzyme-assisted extraction uses cellulases, pectinases or proteases to break down cell walls or matrices, and pulsed electric fields permeabilise cell membranes before extraction. Deep eutectic solvents, mixtures of natural compounds that form low-melting liquids, are being studied as alternatives to organic solvents.
Crude extracts are then concentrated (by evaporation or membranes), purified (by adsorption resins, chromatography or membrane fractionation) and stabilised (by encapsulation, drying or antioxidants), and standardised to a defined content of the active compound. The biorefinery concept recovers several products in a cascade from one by-product, for example oil, then polyphenols, then fibre, then biogas from the residue, so that high-value fractions pay for the whole. Before use in food, extracts must be assessed for safety: contaminants such as pesticide residues, mycotoxins and heavy metals can be concentrated with the bioactives, and many jurisdictions treat new extracts or new sources as novel foods or additives requiring approval. Health claims for bioactive ingredients require scientific substantiation under the claims rules of each market.
Food processing is water-intensive: water is used as an ingredient, for washing raw materials, conveying (flumes), blanching, cooling, steam raising, cleaning and sanitation, and for staff facilities. Cleaning often accounts for a large share of the total. Water intensity, the volume of water used per unit of product (for example litres per kilogram or per litre of product), varies widely between plants making the same product, which shows how much can be saved by good practice. Reducing water use also reduces wastewater volumes, treatment costs, and the energy used to heat and pump water.
A water-reduction programme starts with metering and a water balance, so that each use is known, and then works through measures in order of cost-effectiveness: repairing leaks and fitting automatic shut-off on hoses; dry clean-up of spills and solids before wet cleaning; optimising CIP with recovery of final rinse water for the next pre-rinse, and right-sized spray devices; replacing open hoses with high-pressure, low-volume nozzles; counter-current washing of produce, in which clean water enters at the last stage and flows backward through earlier stages; recirculating cooling water through cooling towers or closed loops; recovering condensate and, in dairies, the water evaporated from milk in evaporators (sometimes called cow water), which after treatment can be reused for cleaning or boiler feed; and changing processes, for example replacing water flumes with dry conveyors. Each change must be checked for food-safety implications.
Water that is reused must be fit for its purpose. Water used as an ingredient or in contact with food must be of potable quality; lower grades may be acceptable for some uses that do not contact food, such as cooling towers, yard washing and toilet flushing. The Codex guidelines for the safe use and re-use of water in food production and processing, adopted in 2023, describe a risk-based, fit-for-purpose approach in which the quality required depends on the intended use and the hazards involved, with treatment, monitoring and verification proportionate to the risk. Reclaimed water from an on-site treatment plant, treated by membrane filtration, reverse osmosis and disinfection, can reach potable quality, but its use in contact with food generally requires approval by the regulator and robust monitoring.
The water footprint, developed by Hoekstra and colleagues, measures the total volume of fresh water used to produce a product along its whole supply chain. It has three components. The blue water footprint is surface water and groundwater consumed (evaporated, incorporated into the product, or returned to a different place); the green water footprint is rainwater stored in soil and used by crops; and the grey water footprint is the volume of fresh water needed to dilute pollutants to meet ambient water-quality standards. For most foods, agriculture dominates the footprint, especially green water for crops, and the factory's own direct use is a small fraction; global average estimates for beef, for example, are of the order of 15 000 litres per kilogram, mostly green water for feed, while those for cereals are of the order of 1500 to 2000 litres per kilogram, with very large variation by region and system. ISO 14046 sets out a life-cycle-based approach to water footprinting that considers impacts, such as water scarcity in the region where water is used, not just volumes. Water stewardship programmes ask food companies to manage water not only within their fences but in the catchments where their plants and suppliers operate.
Food processing uses energy mainly as heat, for cooking, pasteurisation, sterilisation, evaporation, drying, frying and cleaning, and as electricity, for refrigeration and freezing, compressed air, pumps, fans, motors and lighting. Drying and evaporation are among the most energy-intensive operations because they remove water as vapour, needing about 2.3 MJ of latent heat per kilogram of water or more. An energy audit measures energy use by area and process, identifies losses and calculates the costs and savings of improvements, often expressed as specific energy consumption, such as megajoules per tonne of product.
Measures follow from thermodynamics. Heat recovery reuses heat that would otherwise be lost: regenerative sections of plate pasteurisers recover typically 90 per cent or more of the heat by heating incoming cold milk with outgoing hot milk; heat exchangers recover heat from waste water, condensate, exhaust air of dryers and flue gas of boilers; and heat pumps raise low-grade heat from refrigeration condensers or effluents to useful temperatures. In evaporation, multiple-effect evaporators reuse vapour from one effect to heat the next, and mechanical vapour recompression (MVR) compresses the vapour so that it can heat the same effect, using a small amount of electricity instead of much steam. Steam systems are improved by returning condensate, insulating pipes and valves, repairing steam traps and controlling boiler combustion. Electrical savings come from variable-speed drives on pumps and fans, efficient motors, reducing compressed-air leaks, efficient refrigeration with good controls, and efficient lighting. Combined heat and power plants generate electricity and use the waste heat for process steam, raising overall fuel efficiency. Renewable energy, from biogas, biomass residues such as husk and bagasse, solar thermal heat and electricity, and purchased renewable power, reduces fossil fuel use.
A carbon footprint is the total greenhouse gas emissions caused by an organisation or product, expressed as carbon dioxide equivalents (CO₂e) using global warming potentials, which compare the warming effect of a gas over a period, usually 100 years, with that of carbon dioxide; recent IPCC assessments give methane a 100-year GWP of roughly 27 to 30 and nitrous oxide about 273. The Greenhouse Gas Protocol divides corporate emissions into three scopes. Scope 1 covers direct emissions from sources the company owns or controls, such as fuel burned in boilers and vehicles, process emissions and leaks of refrigerants. Scope 2 covers indirect emissions from purchased electricity, steam, heat and cooling. Scope 3 covers all other indirect emissions in the value chain, upstream (purchased raw materials, packaging, transport) and downstream (distribution, use, end-of-life of products and packaging, food waste). For most food companies, scope 3 is by far the largest, dominated by agricultural production of raw materials, through methane from ruminants and rice, nitrous oxide from fertilised soils and carbon dioxide from land-use change; a dairy or meat company's footprint lies mostly on the farms that supply it.
Emissions are calculated as activity data multiplied by emission factors: for example, 200 000 kWh of electricity at a grid emission factor of 0.5 kg CO₂e per kWh gives 100 tonnes CO₂e in scope 2, and emission factors vary greatly between countries and over time as grids change. Refrigerant leaks can be significant, because hydrofluorocarbons have GWPs in the thousands; the Kigali Amendment (2016) to the Montreal Protocol phases down HFCs worldwide, encouraging natural refrigerants such as ammonia, carbon dioxide and hydrocarbons. Product carbon footprints follow standards such as ISO 14067, based on life-cycle assessment (chapter 9). Companies increasingly set reduction targets aligned with climate science, report emissions under mandatory or voluntary disclosure rules, and work with suppliers on farm-level reductions, because factory energy efficiency alone cannot address most of a food product's footprint.
Life-cycle assessment (LCA) evaluates the environmental impacts of a product or service over its life cycle, from extraction of raw materials through production, distribution and use to end-of-life. It is standardised in ISO 14040 (principles and framework) and ISO 14044 (requirements and guidelines), which describe four phases. Goal and scope definition states why the study is done and for whom, the functional unit (the quantified performance of the product to which all results refer, such as 1 kg of packaged cheese at the retail shelf, 1 litre of milk, or 100 g of protein), the system boundary (cradle-to-gate, ending at the factory gate, or cradle-to-grave, including use and disposal), and the impact categories, data and assumptions. The choice of functional unit can change conclusions: comparing foods per kilogram ignores differences in nutrition, which is why per-protein or nutrient-density functional units are sometimes used.
Life-cycle inventory analysis collects data on all inputs (materials, energy, water, land) and outputs (products, co-products, emissions to air, water and soil, wastes) of each process within the boundary, using measured data for the company's own processes (foreground data) and databases for background processes such as electricity and fertiliser production. Life-cycle impact assessment converts inventory flows into contributions to impact categories using characterisation factors: climate change (kg CO₂e), acidification, freshwater and marine eutrophication, photochemical ozone formation, water use or scarcity, land use, resource depletion, ecotoxicity and others. Interpretation identifies the significant issues (hotspots), checks completeness, sensitivity and consistency, and draws conclusions and recommendations within the limits of the study.
Food systems produce many co-products, and the way environmental burdens are shared among them, allocation, strongly affects results. A dairy farm produces milk and meat; a cheese plant produces cheese and whey; a mill produces flour, bran and germ; an oilseed crusher produces oil and meal. ISO 14044 recommends avoiding allocation where possible, by dividing processes into sub-processes or by system expansion (crediting the co-product with the burden of the product it displaces); where allocation is unavoidable, it should reflect physical relationships (such as mass or energy content) or, otherwise, economic value. Mass allocation gives a low-value by-product the same burden per kilogram as the main product, while economic allocation gives it little; choices must be stated and tested in sensitivity analysis. Attributional LCA describes the burdens attributable to a product in a given system; consequential LCA estimates the change in impacts caused by a decision, such as increasing production, including market effects.
Large reviews of food LCAs show consistent patterns. For most foods, agricultural production dominates the impacts, especially for animal products, where feed production, enteric methane and manure are the main sources; processing, packaging, transport and retail are usually smaller but can matter for products with energy-intensive processing (such as powders and frozen foods), air-freighted produce, or heavy packaging. Impacts per kilogram vary widely, from low values for many cereals, pulses and vegetables to high values for ruminant meat, with large variation among producers of the same food, which means that improvement on the farm can be as important as switching products. Food waste matters because all the impacts of producing wasted food are incurred without benefit; preventing waste late in the chain saves the most. LCA has limitations: data gaps and uncertainty, especially for agriculture and land-use change; difficulty in representing biodiversity, soil health and animal welfare; and dependence on methodological choices. Harmonised methods, such as product category rules and the European Union's Product Environmental Footprint method, aim to make results comparable, but comparisons between studies with different assumptions should be made with caution.
A linear economy takes resources, makes products and disposes of them; a circular economy aims to keep materials in use at their highest value and to regenerate natural systems. Its commonly cited principles are to design out waste and pollution, to keep products and materials in use, and to regenerate natural systems. Applied to food, this means preventing surplus and waste, using food for people first, then cascading by-products to their highest-value uses (ingredients, feed, materials, chemicals, energy), returning nutrients and organic matter to soils through compost and digestate, and producing food in ways that restore soils and ecosystems. Bioeconomy and biorefinery strategies extend this to the production of bio-based chemicals and materials, such as bioplastics from starch or lactic acid and packaging from fibres.
Industrial symbiosis links companies so that one's waste becomes another's input: a brewery's spent grain feeds cattle or a bakery's flour; whey from a cheese plant supplies a beverage or ethanol producer; waste heat from one factory warms greenhouses; and food waste from a city supplies an anaerobic digester that returns energy and fertiliser. Redistribution of safe surplus food to people, through food banks, charities and digital platforms connecting businesses and consumers, keeps food at its highest use. Clearer date labelling helps: use-by dates indicate safety for perishable foods, while best-before dates indicate quality, and campaigns and labelling reforms in several countries aim to stop people discarding food that is still safe after its best-before date. Packaging contributes to circularity by protecting food from loss, but also by being designed for reuse, recycling or composting; the balance between preventing food waste and reducing packaging is assessed case by case.
Upcycled foods are made from ingredients that would otherwise not have gone to human consumption, procured and produced through verifiable supply chains, and with a positive environmental impact, in the definition proposed in 2020 by an industry and academic task force; certification schemes now verify such claims. Examples include flours and protein ingredients from brewers' spent grain; snacks and ingredients from fruit and vegetable pulp left after juicing; okara, the soybean residue of soy milk and tofu making, in baked goods; cascara, the dried pulp of the coffee cherry, used for infusions; cocoa fruit pulp, traditionally discarded, used in juices and as a sweetener; aquafaba, the cooking liquid of chickpeas, used as an egg-white substitute; whey beverages; and surplus bread brewed into beer. Some of these ingredients have long histories of use in particular regions but are new in others, so regulators may treat them as novel foods requiring safety assessment before sale; dried coffee cherry pulp, for example, needed such authorisation before it could be sold in the European Union. Upcycled ingredients must meet the same safety and quality standards as any other food: by-products can carry microbial loads, mycotoxins or pesticide residues, and must be handled as food from the point of generation, not as waste that is later reclassified.
Feeding food by-products and surplus to animals is an old practice that recovers nutrients efficiently, but it carries disease risks. Feeding catering waste and kitchen waste containing meat to pigs has spread foot-and-mouth disease, classical swine fever and African swine fever, so it is banned in many countries, including the European Union, while some countries in East Asia allow it under strict controls with heat treatment, producing regulated 'ecofeed'. Former foodstuffs without meat or fish, such as bakery and confectionery surplus, are widely used in feed under feed-safety rules. Insects, especially black soldier fly larvae, can convert organic by-products into protein and fat for feed and frass for fertiliser; the permitted substrates are regulated, often excluding catering waste and manure, to control disease and contaminant risks.
Environmental regulation of food industries rests on principles recognised in international environmental law and national legislation: prevention (avoid harm rather than repair it), precaution (act on credible risks before full scientific certainty), and polluter pays (those who cause pollution bear its costs). The main instruments are permits, standards, economic instruments and information.
Most food factories of any size need an environmental permit or consent from the regulator to discharge wastewater, emit to air, abstract water or handle waste. Permits set emission limit values, conditions on operation and monitoring, and requirements to report. For larger installations, permits are increasingly based on best available techniques (BAT): the European Union's industrial emissions legislation requires installations above certain capacities, including many food, drink and milk plants, to meet BAT-associated emission levels described in a sectoral reference document, and similar technology-based approaches exist in other countries. New plants or major extensions usually require an environmental impact assessment, which examines effects on water, air, soil, noise, odour, traffic, biodiversity and communities, considers alternatives and proposes mitigation, with public consultation. Effluent discharged to a municipal sewer is controlled by a trade-effluent consent from the sewerage operator, often with charges based on volume and strength (COD and solids), so reducing load saves money directly.
Air emissions from food plants include combustion gases from boilers (carbon dioxide, nitrogen oxides, sulphur oxides, particulates), dust from milling and powder handling, odours from rendering, fish meal, coffee roasting and effluent treatment, and refrigerants. Odour is a frequent cause of community complaints and is controlled by enclosure, extraction and treatment with scrubbers, biofilters or thermal oxidisers. Noise from fans, compressors and transport is also regulated near residential areas.
Waste regulation requires businesses to manage waste so that it does not harm the environment or health: to classify it, store it safely, transfer it only to authorised carriers and facilities, and keep records, a principle sometimes called the duty of care. Many countries discourage landfill of organic waste through landfill taxes or bans, require separate collection of food waste from businesses and sometimes households, and promote the waste hierarchy. Several countries have adopted specific food-waste measures: some require large food retailers to donate unsold edible food to charities rather than destroy it, as France did in 2016; others give tax incentives or legal protection to donors, as in Italy and several other countries; and some charge households by the weight or volume of food waste, as in parts of South Korea. Animal by-products are governed by veterinary rules that set how each risk category must be processed or disposed of.
Extended producer responsibility for packaging, now common in Europe and spreading to Asia, Africa and Latin America, makes producers responsible for financing the collection and recycling of the packaging they place on the market, often with fees that vary with recyclability; plastics policies restrict some single-use items and set recycled-content requirements. Environmental reporting is moving from voluntary to mandatory: large companies in an increasing number of jurisdictions must disclose greenhouse gas emissions and other sustainability information, and investors and retailers ask suppliers for data on carbon, water and waste. Environmental management systems certified to ISO 14001 help companies meet these obligations by identifying environmental aspects and legal requirements, setting objectives, controlling operations, preparing for emergencies such as spills, monitoring performance, auditing and reviewing, in the same high-level structure as ISO 9001 and ISO 22000, so that environmental, quality and food-safety management can be integrated. Compliance is not only a legal matter: incidents such as fish kills from an effluent spill or odour nuisance damage reputations and relationships with communities and customers.
A student uses this subject to analyse an effluent sample (BOD, COD, solids), calculate loads and population equivalents, design an equalisation tank or estimate biogas from a COD load, map the waste streams of a pilot plant with a mass balance, and evaluate a by-product such as citrus peel or whey for pectin, oil or protein recovery. Examination questions favour BOD and biogas calculations, treatment stages and named by-product uses.
Five years into a plant role, a technologist runs the effluent plant or manages its contractor, reports to the regulator against the permit, cuts water and energy use with metering and recovery projects, finds outlets for by-products, prepares data for customer sustainability questionnaires, and checks that reused water and by-product ingredients meet food-safety requirements.
A senior operations or sustainability director decides on investments such as an anaerobic digester, MVR evaporators or a whey protein plant, sets targets for food waste, water and carbon across sites, negotiates with suppliers on farm-level emissions, manages permits and community relations, and reports to boards and investors under disclosure rules.
A researcher at this level develops biorefinery processes and green extraction methods, studies microbial communities and kinetics in anaerobic digestion, builds LCA and techno-economic models of valorisation routes, evaluates the safety and functionality of upcycled ingredients, and advises on policy for food loss and waste reduction.
This manual covers food-industry waste, effluent, by-products and sustainability at degree level. It does not give national effluent discharge limits, permit procedures or waste classifications, which vary by jurisdiction, nor detailed design of treatment plants. Global estimates of food loss and waste, water footprints and emissions are given as approximate published figures that are revised over time and carry large uncertainty. Agricultural waste engineering is in Agricultural Engineering, utilities and plant energy systems in food-plant-design-utilities, and extraction chemistry in more depth in food-additives-ingredients and functional-foods-nutraceuticals.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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