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The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor-UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5-10 kg COD m -3 day -1 , the UASB reactor achieved 50-60% COD removal efficiencies. Gas production was 2-3 dm 3 per dm 3 of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability

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.

A nitrification process under low dissolved oxygen (DO) concentration is proposed in a completely stirred biofilm reactor. The reactor was fed with a synthetic wastewater containing 250 mg NH\d4–N/L. A stable nitrite accumulation in the effluent was obtained during >110 days’ operation; NO\d2–N(NO\d2–N+NO\d3–N) in the effluent reached >90% under 0.5 mg DO/L. Ammonium was completely converted and NH\d4–N in the outlet was as low as 5 mg/L. A transient increase of the DO concentration in the reactor induced a complete conversion of ammonia and nitrite to nitrate after only 2 days. A return to a low DO concentration again induced nitrite accumulation. These results show that the nitrite oxidizers were always present in the reactor but were outcompeted at low DO concentration, due to their lower affinity for oxygen, compared with ammonia oxidizers. Nitrite accumulation could also be favored by free nitrous acid accumulation inside the biofilm.

Simultaneous organic carbon and nitrogen removal was studied in a sequencing batch reactor (SBR) fed with synthetic municipal wastewater and controlled at a low dissolved oxygen (DO) level (0.8 mg dm−3). Experimental results over a long time (120 days) showed that the reactor achieved high treatment capacities (organic and nitrogen loading rates reached as high as 2.4 kg COD m−3 d−1 and 0.24 kg NH3-N m3 d−1) and efficiencies (COD, NH3-N and total nitrogen removal efficiencies were 95%, 99% and 75%). No filamentous bacteria were found in the sludge even though the reactor had been seeded with filamentous bulking sludge. Instead, granular sludge, which possessed high activity and good settleability, was formed. Furthermore, the sludge production rate under low DO was less than that under high DO. Significant benefits, such as low investment and less operating cost, will be obtained from the new process. © 2001 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.

Aerobic granular sludge was observed in a Sequencing Batch Reactor (SBR) in which a synthetic urban wastewater containing sodium acetate as an organic substrate was fed, and dissolved oxygen (DO) was controlled at low concentration (0.7–1.0 mg/l) Microscope examination showed that the morphology of the granules was nearly spherical (0.3–0.5 mm in diameter) with a very clear outline. The granular sludge had a good settleability (Sludge Volume Index (SVI) between 80–100 ml/g) and high COD removal and nitrification activities (2.16 g(TOC)/g(SS) · d and 0.24 g(NH 3 -N)/g(SS) · d). With granular sludge, high quality effluent was obtained for treatment of synthetic wastewater under low DO.

Treatment of methanolic wastewater was studied in an anaerobic sequencing batch reactor (ASBR) for a period of 193 days. The results showed that the system worked efficiently when the system volume loading was of 4–8g COD/l. d. Both Methanol concentration and bicarbonate play an important role in the anaerobic conversion of methanol. The route by which methanol was converted into methane had great effect on the COD removal of system. The acetic acid utilization rate increased with the volume loading. When the volume loading was 8g COD/l. d, the acetic acid utilization rate was 5% and the COD removal was over 95%. While the volume loading was 12g COD/l. d, the acetic acid utilization rate was 15.83% and the COD removal is less than 78%. The results of this study suggest that treating methanolic wastewater using anaerobic sequencing batch reactor is feasible.