A2O Processes Research Articles

Enhanced biological nitrogen removal in MLE combined with post-denitrification process and EF clarifier

A modified ludzack ettinger reactor (MLE) combined with a post-denitrification reactor (PDMLE) using electroflotation (EF) as a secondary clarifier was investigated on its feasibility and process performance. Results indicated that higher mixed liquor suspended solids (MLSS) concentrations in bioreactor (5,350 ± 352 mg L(-1)) were maintained via the highly concentrated return sludge (16,771 ± 991 mg L(-1)) from the EF clarifier and the effluent suspended solids (SS) concentrations continued relatively low, representing effluent SS concentration of 1.71 ± 1.16 mg L(-1), compared with GS-A2O process during the operation of four months. The denitrification was improved by combining MLE process with post-denitrification based on endogenous decay (i.e. no additional carbon source was added), resulting in the removal efficiencies of TN were about 91 and 59% for the influent C/N ratio of 10 and 5, respectively, revealing relatively high nitrogen removal as compared with EF-A2O and gravity settling (GS)-A2O processes as a control. The nitrogen balance analysis indicates that pre-denitrification and post-denitrification contributed to 78 and 22% of TN removed, respectively.

Comparative study of protozoan communities in full-scale MWTPs in Beijing related to treatment processes

The potential influence of process principles and system conditions on shaping protozoan community structures in eight full-scale municipal wastewater treatment systems in Beijing, including four process types, i.e., anaerobic/anoxic/aerobic or anoxic/anaerobic/aerobic process (A2O), anoxic/aerobic or anaerobic/aerobic process (AO), oxidation ditch (OD) and sequencing batch reactor (SBR), was evaluated with the aid of cluster analysis and principal components analysis (PCA). The species richness and abundance distribution of protozoa varied significantly with the process types: the A2O ecosystems harbored more diverse protozoan communities with higher relative abundance of crawling and sessile ciliates than the other systems. Cluster analysis revealed that the protozoan community structures were in high coordination with the process types, i.e., different systems with the same process principles exhibited similar community structures. The A2O processes displayed a distinctively higher similarity of protozoan community structures than the AO processes, suggesting that the A2O ecosystems were more stable than those of AO. The PCA analyses demonstrated that swimming and carnivorous ciliates were correlated with poor settleability of sludge, and that amoebae were sensitive to DO level. We therefore concluded that protozoan community structures were primarily shaped by treatment process principles, whilst they were also modified by system conditions in terms of operational properties and water quality.

Improvment of nitrogen and phosphorus removal in the anaerobic-oxic-anoxic-OXIC (AOAO) process by stepwise feeding

This investigation incorporated a stepwise feeding strategy into the biological process containing anaerobic/oxide/anoxic/oxide (AOAO) stages to enhance nitrogen and phosphorus removal efficiencies. Synthetic wastewater was fed into the experimental reactors during the anaerobic and anoxic stages and the substrates/nutrients were successfully consumed without recycling either nitrified effluent or external carbon source. An intrinsic sufficient carbon source developed during the anoxic stage and caused the NOx (NO2-N+NO3-N) concentration to be reduced from 11.85mg/l to 5.65mg/l. The total Kjeldahl nitrogen (TKN) removal rate was between 81.81%∼93.96% and the PO4-P removal ratio ranged from 93%∼100%. The substrate fed into the anaerobic with a Q1 flow rate and a Q2 into the anoxic reactor. The three difference experiments contained within this study produced Q1/Q2 that varied from 7/3, 8/2, and 9/1. The AOAO process saved nearly one-third of the energy compared with typical biological nutrient removal (BNR) system A2O processes.

The kinetic behaviors of simultaneous phosphorus release and denitrification on sludge for BNR processes

Abstract In this study, we investigated the kinetic behaviors of phosphorus release and denitrification on sludge for two biological nutrient removal (BNR) processes, i.e., suspension growth process (A2O) and combined suspension‐biofilm growth process (TNCU) under anoxic condition. The readily biodegradable substrate and nitrate loadings, 20–180 mg HAc‐COD/g MLSS and 4–25 mg NO3‐N/g MLSS respectively, are controlled in a batch reactor for phosphorus release and denitrification of sludge taken from A2O and TNCU processes under various SRT (5, 10 and 15 days) operating conditions. Experimental results indicated that the occurrence of simultaneous phosphorus release and denitrification is a kinetic competition mode under anoxic condition in the presence of a readily biodegradable substrate. Moreover, the available substrate in bulk solution determined the kinetic behaviors of phosphorus release and denitrification. To prevent nitrate inhibition, the sludge is exposed to a C/N ratio higher than 6.1 for phosphorus release. The sludge's phosphorus content (as created by different SRT processes) and initial nitrate loading dominated the kinetics of phosphorus release and denitrification, respectivley. Moreover, the sludge of suspension gorwth process demonstrated a higher phosphorus release potential than the combined suspension‐biofilm growth process. However, the nitrate inhibition is significant for A2O sludge also. Based on proposed phosphorus release rate equation, the rate constant would be reduced by denitrification about 31–67% and 20–45% for A2O and TNCU processes, respectively.