Simultaneous removal of carbon, nitrogen and phosphorus from wastewater bycoupling two-step anaerobic digestion with a sequencing batch reactor

The objective of this study was to develop an integrated process for simult aneous removal of carbon, nitrogen and phosphorus from industrial wastewate rs. The process consisted of a-two step anaerobic digestion reactor, for ca rbon removal, coupled with a sequencing batch reactor (SBR) for nutrient re moval. In the proposed process, carbon is eliminated into biogas by anaerob ic digestion: acidogenesis and methanogenesis. The volatile fatty acids (VF A) produced during the first step of anaerobic digestion can be used as ele ctron donors for both dephosphatation and denitrification. In the third rea ctor (SBR) dephosphatation and nitrification are induced through the applic ation of an anaerobic-aerobic cycle. This paper describes the first trials and experiments on the SBR and a period of 210 days during which the SBR wa s connected to the acidogenic and methanogenic reactors. It was shown that nitrification of ammonia took place in the SBR reactor, during the aerobic phase. Furthermore, denitrification and VFA production were achieved togeth er in the acidogenic reactor, when the efflux of nitrates from the SBR reac tor was added to the first reactor influx. The proposed process was fed wit h a synthetic industrial wastewater, the composition of which was: total or ganic carbon (TOC) = 2200 mg dm(-3), total Kjeldahl nitrogen (TKN) = 86 mg dm(-3), phosphorus under phosphate form (P-PO4) = 20 mg dm(-3). In these co nditions, removals of carbon, nitrogen and phosphorus were 98%, 78% and 95% respectively. The results show that the combination of the two-step anaero bic digestion reactor and an SBR reactor is effective for simultaneous carb on, nitrogen and phosphorus removal. Reactor arrangements enabled zones of bacterial populations to exist. Complete denitrification occurred in the ac idogenic reactor and hence the anaerobic activity was not reduced or inhibi ted by the presence of nitrate, thus allowing high TOC removal. Stable phos phorus release and phosphorus uptake took place in the SBR after coupling o f the three reactors. A fast-settling compact sludge was generated in the S BR with the operational conditions applied, thus giving good separation of supernatant fluid. The benefits from this process are the saving of (i) an external carbon source for denitrification and phosphorus removal, (ii) a r eactor for the denitrification step. (C) 1998 Society of Chemical Industry.