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A four stage pilot plant of step-feed biological nutrient removal (BNR) was employed to investigate reactor performance and process stability. The results obtained showed that step-feed BNR is efficient and cost-effective for nitrogen and carbonaceous removal from municipal wastewater. The total average removal efficiencies of COD, NH3-N, TN and TP could reach as high as 89.5, 97.8, 73 and 75%, respectively, with 50% of return activated sludge (RAS), 9 h of hydraulic retention time (HRT) and 20 d of sludge retention time (SRT). Step-feed BNR is an alternative and effective technology of nutrient removal for municipal wastewater treatment.

Biological denitrification was studied in an SBR to investigate the performance. The experimental results showed that granular sludge with high activity and good settling ability can be developed smoothly in the reactor. With the granular sludge, high nitrate loading rate (0.48 kg NO3-N dm−3 d−1) and removal efficiency (more than 99%) can be achieved. Scanning electronic microscope examination showed that only rod-shape bacteria existed on and within the granules, which confirmed indirectly that filamentous bacteria do not utilize nitrate and nitrite as electron acceptors. SBR is an alternative and effective technology for biological denitrification.

The effects of colloidal organic matter on nitrification and the composition of extracellular polymeric substances (EPS) in biofilms were studied in two parallel bench-scale biological aerated filters (BAFs) fed with different organic carbon sources. The study filter used starch and glucose to model colloidal and soluble organic carbon, respectively, while the control filter used glucose as the sole organic carbon source. Studies with different COD/NH4+ (C/N) ratios (0.5-6.0) showed that the increase in organic matter in the influent resulted in the displacement of nitrification from the bottom to the upper part of filter bed. It was observed that the greater reduction in nitrification was caused by colloidal organic matter rather than by soluble organics at the same COD concentration. The starch hydrolysis took place in the bottom 40cm of the filter bed, which implied that hydrolysis of colloidal organic matter into smaller molecules could not be the limiting step of its oxidation in the biofilm. In addition, biofilm surface morphology and EPS composition were subject to different substrate conditions. Polysaccharide was the primary and protein the minor component of the EPS extract. In the study filter, the protein content of EPS diminished from the bottom to the upper layer of the filter bed, which was strongly correlated to the hydrolysis of colloidal organic matter. (C) 2002 Society of Chemical Industry.

High ammonium nitrification was studied in a sequencing batch reactor (SBR) with two different oxygen supply methods: controlled oxygen supply rates (dissolved oxygen [DO] in the reactor controlled between 2 and 3 mg/L) and uncontrolled oxygen supply rates (DO in the reactor-uncontrolled and changed ambiently with oxygen use rate). Experimental results showed that oxygen supply methods have significant effects on SBR performance for high ammonium nitrification. With the controlled oxygen supply method, ammonium and nitrite oxidations took place simultaneously. With the uncontrolled oxygen supply method, ammonium oxidation proceeded smoothly during the low DO period of a cycle; however, nitrite oxidation was at first completely inhibited at low-DO but recovered during the high DO period of the same cycle. Ammonium and nitrite were oxidized sequentially during a cycle in SBR. Ammonium oxidizers developed an ability to endure the fluctuation of DO, but nitrite oxidizers did not. Extensive starvation under high DO concentrations plays an important role in ammonium oxidation under low DO conditions.