Question

A regional STP handles wastewater from 22,000 people where the per capita flow is assumed to be 380 L/person/day. This STP comprises (in series) a primary settler, a trickling filter, two facultative ponds, and a mature constructed wetland. The table below gives typical values (all in mg/L) for the overflow stream after the primary settler (APS) and for the final treated effluent (FTE). Parameter APS FTE Suspended solids 120 2 Biochemical oxygen demand 130 3 Total nitrogen (as N) 30 2 Total phosphorus (as P) 6 1 The observed yield (Yob) for this STP is 0.45 mg biomass per mg substrate (i.e. BOD) consumed. (i) How much biomass is produced (in kg/day) in this STP after the primary settler? (ii) Biomass may be represented as C60H87O23N12P. Estimate the weight percentage of N in the biomass, as well as the weight percentage of P in the biomass. Note that there is a table of atomic weights on the first page of this examination paper. (iii) Using the above results, determine what percentage of the N and P in the primary settler overflow are taken up into the biomass produced within this STP. (iv) What percentage of the N and P in the primary settler overflow leaves the STP in the final treated effluent? (v) By carrying out a mass balance, determine how much of the nitrogen (in kg/day) in the primary settler overflow stream is not taken up into new biomass or leaves in the FTE stream. Comment on what might be happening to this ‘missing’ nitrogen.

Answer 1

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6mg of ォ. But there P in 1L N in biomoss ik Ci-291) x too the FTE have. d om that leaves fey masy overflou, we have Fom the ri 30 (2.130) 치00- 6-69-j. Thus the TE ve have a가てプ that leaves Pes L From coates, Cieo-2s. 3-66 )、/- N that i nerthes taken neu bioma and ho doesH up in the

Thus, for 구0.03-/- unacco unted goes Total N uraccounted pex lbe 21-ooq mgIL o-aco 3 Χ 30 mg But hee ae 83 oooo L h uaoder thus g3oo0o x 21-009 C21.0o/loocook Thank ou