State dairy development department posts · India · State public service commissions (e.g. Kerala PSC)
Original practice questions written to the published syllabus · not past papersCharacterising and treating dairy wastewater, sludge and emissions, and measuring the environmental footprint of milk.
In the exams: ICAR AICE subject 34 Unit 4 (BOD and COD in dairy waste) and subject 35b Unit 1 (EMS); ICAR AIEEA-PG group 16 (disposal of dairy waste)
How our questions for State dairy development department posts spread across the units of Dairy Effluent Treatment & Environmental Management. Difficulty: 20 easy, 22 medium, 1 hard.
| Sources and characteristics of dairy effluent | 7 | |
| Aerobic treatment: activated sludge and its variants | 6 | |
| Preliminary and primary treatment: screening, equalisation, dissolved air flotation | 5 | |
| Anaerobic treatment and biogas | 4 | |
| Discharge standards and permits | 4 | |
| Environmental management systems: ISO 14001 | 4 | |
| BOD, COD, fats-oil-grease and nutrient measurement | 3 | |
| Sludge handling and disposal | 3 | |
| Water recovery from cow water and condensate | 3 | |
| Life-cycle assessment and carbon footprint of dairy products | 2 | |
| Nutrient removal and tertiary treatment | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
An effluent flow of 500 m³/day has a COD of 3,000 mg/L. What is the daily COD load?
C. 1,500 kg/day
Load = 500 m³ × 3,000 g/m³ = 1,500,000 g = 1,500 kg/day (mg/L equals g/m³).
Further reading: APHA, Standard Methods for the Examination of Water and Wastewater
A plant processing 500,000 L of milk a day loses 1% to drain. Taking milk BOD as 100,000 mg/L, what BOD load does this add?
D. 500 kg/day
5,000 L × 100 g/L = 500,000 g = 500 kg BOD/day.
Further reading: Tetra Pak, Dairy Processing Handbook
A reactor's influent COD is 4,000 mg/L and its effluent COD is 800 mg/L. What is the COD removal?
D. 80%
(4,000 − 800) ÷ 4,000 = 80%.
Further reading: Metcalf & Eddy, Wastewater Engineering
What does an effluent audit usually reveal about where the load comes from?
C. A few events cause most of it
Tank emptying, changeovers, desludging and spills dominate; targeting them gives most of the savings.
Further reading: Tetra Pak, Dairy Processing Handbook
In most countries, which kind of law is the main basis for controlling dairy effluent discharges?
D. A water-pollution control law
Water-pollution control (or general environmental protection) legislation requires discharge permits and sets effluent standards. Food safety law governs the product, not the effluent; boiler and energy laws cover other utilities.
Further reading: Manual chapter: Discharge standards and permits
A dairy's permit limits BOD to 100 mg/L for discharge to surface water. If the plant discharges 800 m³ of treated effluent a day, what is the maximum BOD load it may release?
B. 80 kg/day
Load (kg/day) = concentration (mg/L) × flow (m³/day) ÷ 1,000 = 100 × 800 ÷ 1,000 = 80 kg/day. 80,000 is the load in grams per day mistaken for kilograms; 8 and 800 are decimal slips.
Further reading: Manual chapter: BOD, COD, fats-oil-grease and nutrient measurement
Why do trade effluent charges based on COD encourage plants to cut load?
D. Lower load means lower fees
Charges scale with volume and strength, so reducing COD saves money directly.
Further reading: Metcalf & Eddy, Wastewater Engineering
Which aerobic option suits a rural dairy with plenty of land and low budget?
C. Aerated lagoons
Lagoons are cheap but need land and can smell if overloaded.
Further reading: Metcalf & Eddy, Wastewater Engineering
What dissolved oxygen is typically maintained in an aeration tank?
D. Near 2 mg/L
About 2 mg/L supports aerobic activity without wasting blower energy.
Further reading: Metcalf & Eddy, Wastewater Engineering
Why can a milk powder plant become a net water exporter?
A. Milk is 87% water
Water evaporated from milk can exceed fresh water drawn by the plant.
Further reading: Tetra Pak, Dairy Processing Handbook
Ten here, 43 in the app. The Laisha app has every practice question we have written to State dairy development department posts in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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