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Effects of urine separation and treatment
Expanded Title:With complete urine separation, the need for nitrification and denitrification falls away at activated sludge plants, which would be operated at short sludge ages (5 days) with anaerobic phosphate release and aerobic phosphate uptake. Treatment of undiluted source separated urine in a sequencing batch reactor could be described in terms of the normal activated sludge model stoichiometry. The specific process rates were however less than normal activated sludge kinetics, due to salinity of urine, as well as extreme high free ammonia and nitrous acid concentrations. Still, due to the small volume of urine (by comparison to the overall domestic wastewater production), the lower rate is not of concern. At least one third of the nitrogen in urine can be removed over nitrite by utilizing the COD in urine. The resulting ammonium-nitrite mixture is the ideal feed for an Anammox process that removes nitrogen without the need for organic carbon. An alternative systems, which consists of treating yellow water from no-mix toilets with waste activated sludge, was investigated in an anoxic-aerobic digester. This is a fairly simple system, which could augment existing overloaded treatment works immediately, or eventually be developed to remove all nitrogen in a side stream process. Although urine makes up less than one percent of the volume of wastewater, it contains around 50% of the total phosphate load and up to 80% of the nitrogen load in wastewater. The impact of urine diversion on BNRAS processes was investigated in a laboratory scale reactor with a University of Cape Town (UCT) BNR system configuration, receiving mixes of grey and brown wastewater collected separately at the CSIR in Stellenbosch. Interestingly, the grey water and brown water collected for experiments had lower overall concentrations than that measured initially at CSIR. Out of 13 batches, brown water concentrations were 2,238 mgCOD/l, 166 mgTKN/l and 50 mgP/l. Grey water concentrations were 1,434 mgCOD/l, 65 mgTKN/l and 27 mgP/l. After reaching steady state, the laboratory-scale UCT system was operated for 90 days at a sludge age of 20 days and a temperature of 20ºC. Effluent ammonia and nitrate concentrations (both <1 mgN/l) and aerobic batch test on sludge harvested from the aerobic reactor revealed the nonexistence of nitrifers in the system treating a 50:50 (by volume) grey and brown water mix. A series of batch tests were done, which pointed to 6 factors to prove the non-existence of nitrifiers in the system, which included (i) no nitrite or nitrate in the effluent (ii) no nitrate generation when fed with excess ammonium in batch tests (iii) no decrease in alkalinity (iv) phosphate release in the anoxic compartment (v) measure oxygen uptake rate yielded a good COD balance and (vi) a low nitrogen fraction of the sludge produced. This meant that nearly all N was used for biological growth and no nitrate was produced, and the P removal proceeded via the normal biological excess P removal (BEPR). In fact, the batch tests indicated that the system might have been nitrogen deficient. The removal efficiencies of the system were 86%; 90% and 93% for Organics (COD), Total Kjeldahl Nitrogen (TKN) and Total Phosphorus (TP) respectively and the effluent concentrations were 85.3 mgCOD/l, 2.9 mgTKN/l, 0 mgNO3-N/l and 1.3 mg TP/l. These removal performances were all better than those achieved in a control system, with exact design parameters and an equivalent COD feed, from a real domestic wastewater treatment works. A second system was operated according to the Johannesburg (JHB) process configuration, which also received a 50:50 mixture of grey and brown water. The JHB process is similar to the UCT process, but includes an anoxic zone in the return activated sludge stream, to remove any nitrate before entering the anaerobic zone. The mass balances showed that if all the degradable COD was utilized, then the very low effluent standards of 0.1 mgP/l could be achieved in both UCT and JHB process configurations. Furthermore, based on the mass of COD load on a wastewater treatment works, the reactor can be reduced by 50% if urine was collected separately. From the perspective of an existing system, an activated sludge reactor basin could treat double the design load if urine was collected separately at source!
Date Published:01/02/2014
Document Type:Research Report
Document Subjects:Wastewater Management - Domestic, Sanitation - Waterborne sanitation
Document Keywords:Municipality
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:TT 586/13
ISBN No:978-1-4312-0504-2
Authors:Wilsenach JA; McMillan M; Mbaya A; Motlomelo KG; Anderson C; Pascal A; Brown S; Germanis J; Mashego MR; Du Plessis JA; Ekama GA
Project No:K5/1824
Document Size:3 899 KB
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