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The primary objectives of this study were to identify the effectiveness of hydrazine on partial nitrification in a sequencing batch reactor when treating low-strength ammonia wastewater and to investigate its impact mechanism. Partial nitrification was successfully initiated and maintained by dosing with hydrazine, and the short- and long-term effects of hydrazine on partial nitrification and microbial bioactivity were investigated. The results showed that dosing with a moderate amount of hydrazine improved the nitrite accumulation rate with little effect on the ammonia conversion rate. Both the short- and long-term tests showed the optimum hydrazine dosage was 7.5 mg/L. In the long-term tests, dosing with 7.5 mg/L of hydrazine led to an ammonia conversion rate and nitrite accumulation rate of 99.10% and 93.24%, respectively. The change in the mixed liquid suspended solids (MLSS) and mixed liquid volatile suspended solids (MLVSS) in the long-term tests showed that, although dosing with hydrazine influenced the biochemical activity of the sludge, the MLVSS/MLSS increased after an initial decrease. High-throughput analysis showed that Thauera, Nitrosomonas, and Denitratisoma were the dominant bacteria in the system dosed with 7.5 mg/L of hydrazine, which may explain the high nitrite accumulation. Analysis of the mechanism showed that nitrite-oxidizing bacteria were more inhibited by hydrazine dosing than ammonium-oxidizing bacteria. [ABSTRACT FROM AUTHOR]

In this paper, a state-space model based on an activated sludge model (ASM) was developed and an iterative learning control (ILC) algorithm for a sequencing batch reactor (SBR) are proposed for optimal nitrogen removal. A reduced-order state-space model of an ASM was derived by lumping some components of an ASM in the aerobic and anoxic phase, and then the ILC algorithm was suggested as a batch tracking control that worked in a repetitive mode of an SBR using the reduced state-space model. A new algorithm of ILC was suggested to control dissolved oxygen (DO) concentration in the aerobic phase and to find the optimal amount of external carbon, which was added to the anoxic phase in an SBR. By using information from previous batches, a suitable ILC control action was found iteratively. Simulations clearly represented that the ILC algorithm in the aerobic phase showed much better control performance of DO concentration than the conventional PID control, and could find a minimum amount of added external carbon for the anoxic phase in an SBR, which reduced the total cost by 35.6%. Results showed that the ILC model was derived from the microbiological concept of an ASM, and the learning ability of ILC could reduce the error of the controller. [ABSTRACT FROM AUTHOR]

A treatment system using a combined biological engineering process has been developed to effectively treat municipal solid waste (MSW) landfill leachate. The process combines an up-flow anaerobic sludge blanket (UASB), a sequencing batch reactor (SBR), a continuous micron filtration (MF), and reverse osmosis (RO) technologies to treat leachate from the Guangzhou Xingfeng Municipal Solid Waste Sanitary Landfill, which accepts about 5,500–6,500 tons of municipal solid wastes and generated around 1,700 m3 of leachate each day. The combined technology has achieved successful operational results with average removal efficiencies for CODCr, BOD5, and total nitrogen of 99.8, 99.8, and 99.5%, respectively. The effluent quality consistently meets the nonpotable water reuse standard. [ABSTRACT FROM AUTHOR]

High salinity synthetic wastewater was treated in a four-step sequencing batch reactor (SBR) for nutrient removal at different salt (NaCl) concentrations by using Halobacter-added and Halobacter-free activated sludge cultures. Salt (NaCl) concentration was varied between 0 and 6% (w/v). The sequencing batch operation for nutrient removal consisted of anaerobic, oxic, anoxic, and oxic phases with hydraulic residence times (HRT) of 1/3/1/1 h and a settling phase of 45 min. Sludge age (SRT) was kept constant at 10 days in all experiments. Effects of salt content on percent removals of COD, NH-N and PO-P were investigated for both cases. Percent COD, NH-N and PO-P removals decreased with increasing salt content for both cultures, resulting in high effluent nutrient levels and high sludge volume indexes (SVI) at high salt contents. However, Halobacter-added activated sludge culture resulted in considerably higher percent nutrient removals, especially at salt contents above 2%. Nearly, 73% COD, 51% NH-N, 31% PO-P were removed from 5% salt containing wastewater with the Halobacter-added activated sludge, whereas percent removals were 47% COD, 36% NH-N, and 21% PO-P for the Halobacter-free culture in the SBR. [ABSTRACT FROM AUTHOR]

Nutrient removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different 2,4 dichlorophenol (DCP) concentrations. The nutrient removal process consisted of anaerobic, oxic, anoxic, and oxic phases with hydraulic residence times (HRT) of 1/ 3/ 1/1 h and a settling phase of 45 min. Solids retention time (SRT) was kept constant at 10 days in all experiments. Initial dichlorophenol concentrations were varied between 0 and 240 mg/L at eight different levels. Effects of dichlorophenol on removal of COD, NH4-N, and PO4-P and on effluent nutrient concentrations were investigated. Dichlorophenol was almost completely degraded up to 123 mg/L influent concentration. Adverse effects of dichlorophenol on COD removal were almost negligible for DCP concentrations below 123 mg/L. About 96% COD, 46% NH4-N, and 22% PO4-P removals were obtained at a DCP concentration of 123 mg/L. The sludge volume index (SVI) changed in a range of 59 to 93 mL/g for DCP concentrations below 123 mg/L, which increased to 142 mL/g at a DCP level of 240 mg/L. [ABSTRACT FROM AUTHOR]