1. In which year was the term Biosolids introduced?
a) 1990
b) 1995
c) 1998
d) 2000
Explanation: The term “biosolids” was introduced by the Water Environment Federation in the U.S. in 1998. However, some people argue that the term is a form of “propaganda” with the aim to hide the fact that sewage sludge may also contain substances that could be harmful to the environment when the treated sludge is applied to land
2. What is the first step in the sewage treatment process?
a) Dewatering
b) Thickening
c) Phosphorus recovery
d) Digestion
Explanation: Thickening is often the first step in a sludge treatment process. Sludge from primary or secondary clarifiers may be stirred (often after addition of clarifying agents) to form larger, more rapidly settling aggregates.
3. What is the amount of solids released into wastewater by human beings?
a) 30 gpcd
b) 40 gpcd
c) 60 gpcd
d) 70 gpcd
Explanation: Humans deposit about 70 g per capita per day of solids into wastewater. With ‘garbage grinders’, this can reach 100g per day. The impurities present in the wastewater must either be transformed into innocuous end-products or be effectively separated from the effluent stream.
4. What is the percentage of aerobically digested sludge?
a) 0.2-0.5
b) 0.3-0.6
c) 1.0-2.0
d) 1.5-3.0
Explanation: The solids concentration in thickened, aerobically digested sludge is generally in the range 1.0% – 2.0% as determined by digester design and operation.
5. Ws = Wsp + Wss
What does Wsp stand for in the above equation?
a) Total dry solids
b) Raw primary solids
c) Suspended solids
d) Polluted solids
Explanation: Waste solids production in primary and secondary processing can be estimated using the calculation above. Ws stand for total dry solids. Wsp stands for raw primary solids. Wss stands for secondary biological solids.
6. Sludge from the primary clarifier is ______
a) Brown and flocculant like appearance
b) Dark in colour
c) Gray and slimy
d) Dark brown in colour
Explanation: Sludge from the primary clarifier is gray in colour. It is also slimy in appearance. Also it has an offensive odour.
7. How does the chemical sludge appear?
a) Gray in colour and not slimy
b) Brown and flocculant like appearance
c) Red/grayish brown
d) Black in colour
Explanation: In case the sludge contains iron it is red in colour. In case it is lime sludge, it is grayish brown in colour. This sludge also has an objectionable odour.
8. How does the activated sludge appear?
a) Gray
b) Red
c) Brown and flocculant like appearance
d) Greasy
Explanation: The activated sludge is brown in colour. It also has flocculant like appearance. If the colour is dark, then the sludge has approached septic condition
9. What is the % of dry solids assumed for a primary sludge from a settling tank at the outlet?
a) 12%
b) 5-7%
c) 8%
d) 9-11%
Explanation: The percentage of dry solids for a primary sludge is assumed as 5-7% at the outlet. In most cases, it is considered as 6%. In the case of sludge is from the flocculator or clarifier the percentage of solids is considered as 2-4%.
10. What is the percentage of dry solids assumed for the sludge at the outlet of a centrifuge?
a) 10-15%
b) 1-3%
c) 4-8%
d) 9-12%
Explanation: The percentage of dry solids assumed for the sludge at the outlet of a centrifuge is 4-8%. In most cases, this is considered as 5%. Even for a Gravity belt thickener with the addition of polyelectrolyte the percentage of dry solids is considered as 4-8%.