Biological treatment of source separated urine in a sequencing batch reactor

[摘要] ENGLISH ABSTRACT: Urine contains up to 80% of nitrogen, 50 % of phosphates and 90 % of potassium of the totalload in domestic wastewater but makes up less than 1% of the total volume (Larsen et al.,1996). The source separation and separate treatment of this concentrated waste stream canhave various downstream advantages on wastewater infrastructure and treated effluentquality. The handling of undiluted source separated urine however poses various challengesfrom the origin onward. The urine has to be transported to a point of discharge and ultimatelyhas to be treated in order to remove the high loads of organics and nutrients. Wilsenach (2006)proposed onsite treatment of source separated urine in a sequencing batch reactor beforedischarging it into the sewer system.This study focused on the treatment of urine in a sequencing batch reactor (SBR) primarily forremoval of nitrogen through biological nitrification-denitrification. The aim of the study was todetermine nitrification and denitrification kinetics of undiluted urine as well as quantification ofthe stoichiometric reactions. A further objective was to develop a mathematical model fornitrification and denitrification of urine using experimental data from the SBR.The SBR was operated in 24 hour cycles consisting of an anoxic denitrification phase and anaerobic nitrification phase. The sludge age and hydraulic retention time was maintained at 20days. pH was controlled through influent urine during volume exchanges. Undiluted urine forthe study was obtained from a source separation system at an office at the CSIR campus inStellenbosch. Conditions in the reactor were monitored by online temperature, pH and ORPprobes. The OUR of the system was also measured online.One of the main challenges in the biological treatment of undiluted urine was the inhibitingeffect thereof on nitrification rate. The anoxic mass fraction was therefore limited to 17 % inorder to allow longer aerobic phases and compensate for the slow nitrification rates. Volumeexchanges were also limited to 5% of the reactor volume in order to maintain pH within optimalrange.Samples from the reactor were analysed for TKN, FSA-N, nitrite-N, nitrate-N and COD. From theanalytical results it was concluded that ammonia oxidising organisms and nitrite oxidisingorganism were inhibited as significant concentrations of ammonia-N and nitrite-N were presentin the effluent. It was also concluded that nitrite oxidising organisms were more severelyinhibited than ammonia oxidising organisms as nitrate-N was present in very lowconcentrations in the effluent and in some instances not present at all.Ultimately the experimental system was capable of converting 66% of FSA-N to nitrite-N/nitrate-N of which 44% was converted to nitrogen gas. On average 48% of COD wasremoved.A mathematical model was developed in spreadsheet form using a time step integrationmethod. The model was calibrated with measured online data from the SBR and evaluated bycomparing the output with analytical results. Biomass in the model was devised into threegroups, namely heterotrophic organisms, autotrophic ammonia oxidisers (AAO) andautotrophic nitrite oxidisers (ANO). It was found that biomass fractionation into these threegroups of 40% heterotrophs, 30% AAO and 30% ANO produced best results.The model was capable of reproducing the general trends of changes in substrate for thevarious organism groups as well as OUR. The accuracy of the results however varies and nearexactresults were not always achievable. The model has some imperfections and limitationsbut provides a basis for future work.

[发布机构] Stellenbosch University