Microbial kinetic analysis of three different types of EBNR process

A novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) for advanced nitrogen removal from domestic sewage

To achieve advanced nitrogen removal from actual municipal sewage, a novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) was developed. The reactor was used to treat actual domestic sewage and the nitrogen removal capacity of the sludge regeneration zone (R zone) was investigated during the long-term operation. The best performance was obtained at the R zone's Oxidation-Reduction Potential (ORP) of -50±30 mV and hydraulic residence times (HRT) of 1.2 hr. The average effluent COD, TN, NH₄⁺-N and NO₃^--N of the R-MAO process were 18.0±2.3, 7.5±0.6, 1.0±0.5 and 4.6±0.4 mg/L, respectively, with the corresponding removal efficiency of COD, TN and NH₄⁺-N were 92.9%±1.0%, 84.1%±1.5% and 97.5%±1.1%. Compared to the sole MAO system, the TN removal efficiency of the R-MAO increased by 10.1%. Besides, under the optimal conditions, the contribution of the R zone in the R-MAO that removal COD, TN, NH₄⁺-N and NO₃^--N were 0.36, 0.15, 0.032 and 0.82 g/day. High-throughput sequencing results showed that uncultured_bacterium_f_Burkholderiaceae (5.20%), OLB8 (1.04%) and Ottowia (1.03%) played an important role in denitrification in the R zone. This study provided effective guidance for the design and operation of the R-MAO process in domestic sewage treatment.

Efficient model calibration method based on phase experiments for anaerobic-anoxic/nitrifying (A2N) two-sludge process

A systematic calibration and validation procedure for the complex mechanistic modeling of anaerobic-anoxic/nitrifying (A2N) two-sludge system is needed. An efficient method based on phase experiments, sensitivity analysis, and genetic algorithm is proposed here for model calibration. Phase experiments (anaerobic phosphorus release, aerobic nitrification, and anoxic denitrifying phosphate accumulation) in an A2N sequencing batch reactor (SBR) were performed to reflect the process conditions accurately and improve the model calibration efficiency. The calibrated model was further validated using 30 batch experiments and 3-month dynamic continuous flow (CF) experiments for A2N-SBR and CF-A2N process, respectively. Several statistical criteria were conducted to evaluate the accuracy of model predications, including the average relative deviation (ARD), mean absolute error (MAE), root mean square error (RMSE), and Janus coefficient. Visual comparisons and statistical analyses indicated that the calibrated model could provide accurate predictions for the effluent chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP), with only one iteration.

An efficient process for wastewater treatment to mitigate free nitrous acid generation and its inhibition on biological phosphorus removal

Free nitrous acid (FNA), which is the protonated form of nitrite and inevitably produced during biological nitrogen removal, has been demonstrated to strongly inhibit the activity of polyphosphate accumulating organisms (PAOs). Herein we reported an efficient process for wastewater treatment, i.e., the oxic/anoxic/oxic/extended-idle process to mitigate the generation of FNA and its inhibition on PAOs. The results showed that this new process enriched more PAOs which thereby achieved higher phosphorus removal efficiency than the conventional four-step (i.e., anaerobic/oxic/anoxic/oxic) biological nutrient removal process (41 ± 7% versus 30 ± 5% in abundance of PAOs and 97 ± 0.73% versus 82 ± 1.2% in efficiency of phosphorus removal). It was found that this new process increased pH value but decreased nitrite accumulation, resulting in the decreased FNA generation. Further experiments showed that the new process could alleviate the inhibition of FNA on the metabolisms of PAOs even under the same FNA concentration.

Behaviors of biomass and kinetic parameter for nitrifying species in A²O process at different sludge retention time

The effect of sludge retention time (SRT) on biomass, kinetic parameters, and stoichiometric parameters of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in anaerobic/anoxic/oxic (A(2)O) process were explored in this study. The results showed that the growth rate constants were 1.52, 1.22, and 0.85 day(-1), respectively, for AOB, those were 1.59, 1.19, and 0.87 day(-1), respectively, for NOB when SRT was 20, 10, and 5 days. The lysis rate constants of AOB and NOB were 0.14 and 0.09 day(-1), respectively. The yield coefficients were 0.23 and 0.22, respectively, for AOB and NOB. They did not change with SRT obviously. The biomass of AOB was 50.94, 26.35, and 14.68 mg L(-1), respectively, and the biomass of NOB was 116.77, 60.00, and 44.25 mg L(-1), respectively, at SRT of 20, 10, and 5 days. When SRT diminished from 20 to 5 days, the biomass of AOB and NOB diminished by 36.26 and 75.52 mg L(-1), respectively. The removal efficiency of NH4 (+)-N diminished by 68.9 %. The removal efficiency of total nitrogen diminished by 42.9 %.

Enhanced nutrient removal in a modified step feed process treating municipal wastewater with different inflow distribution ratios and nutrient ratios

A pilot-scale modified step feed process was proposed to enhance organics and nutrient (N and P) removal performance from municipal wastewater. It combined University of Cape Town (UCT) and step feed process. Effects of inflow distribution ratios and nutrients ratios were investigated. The highest removal efficiencies of 89% for chemical oxygen demanding (COD), 88% for total nitrogen (TN) and 93% for phosphorus were obtained, respectively, at the inflow distribution ratio of 40:30:30%. The phosphorus removal exhibited an upward trend with the increasing of influent COD/P and TN/P, and the nitrogen removal had a positive correlation with influent COD/TN. In addition, aerobic simultaneous nitrification and denitrification and anoxic denitrifying phosphorus uptake made a distinct contribution to enhance nutrient removal. The proposed system was demonstrated to be an attractive enhanced biological nutrient removal process for wastewater treatment plants due to relatively high nutrient removal, robust sludge settleability and energy savings.

Novel modeling concept for evaluating the effects of cadmium and copper on heterotrophic growth and lysis rates in activated sludge process

A new modeling concept to evaluate the effects of cadmium and copper on heterotrophic growth rate constant (mu(H)) and lysis rate constant (b(H)) in activated sludge was introduced. The oxygen uptake rate (OUR) was employed to measure the constants. The results indicated that the mu(H) value decreased from 4.52 to 3.26 d(-1) or by 28% when 0.7 mg L(-1) of cadmium was added. Contrarily the b(H) value increased from 0.31 to 0.35 d(-1) or by 11%. When adding 0.7 mg L(-1) of copper, the mu(H) value decreased to 2.80 d(-1) or by 38%. The b(H) value increased to 0.42 d(-1) or by 35%. After regression, the inhibitory effect was in a good agreement with non-competitive inhibition kinetic. The inhibition coefficient values for cadmium and copper were 1.82 and 1.21 mg L(-1), respectively. The relation between the b(H) values and heavy metal concentrations agreed with exponential type well. The heavy metal would enhance b(H) value. Using these data, a new kinetic model was established and used to simulate the degree of inhibition. It was evident that not only the inhibitory effect on mu(H) but also that the enhancement effect on b(H) should be considered when heavy metal presented.

Comparisons of grey and neural network prediction of industrial park wastewater effluent using influent quality and online monitoring parameters

In this study, Grey model (GM) and artificial neural network (ANN) were employed to predict suspended solids (SSeff) and chemical oxygen demand (CODeff) in the effluent from a wastewater treatment plant in industrial park of Taiwan. When constructing model or predicting, the influent quality or online monitoring parameters were adopted as the input variables. ANN was also adopted for comparison. The results indicated that the minimum MAPEs of 16.13 and 9.85% for SSeff and CODeff could be achieved using GMs when online monitoring parameters were taken as the input variables. Although a good fitness could be achieved using ANN, they required a large quantity of data. Contrarily, GM only required a small amount of data (at least four data) and the prediction results were even better than those of ANN. Therefore, GM could be applied successfully in predicting effluent when the information was not sufficient. The results also indicated that these simple online monitoring parameters could be applied on prediction of effluent quality well.

A modified UCT method for biological nutrient removal: configuration and performance

A pilot-scale prototype activated sludge system is presented, which combines both, the idea of University of Cape Town (UCT) concept and the step denitrification cascade for removal of carbon, nitrogen and phosphorus. The experimental set-up consists of an anaerobic selector and stepwise feeding in subsequent three identical pairs of anoxic and oxic tanks. Raw wastewater with influent flow rates ranging between 48 and 168 l d(-1) was fed to the unit at hydraulic residence times (HRTs) of 5-18 h and was distributed at percentages of 60/25/15%, 40/30/30% and 25/40/35% to the anaerobic selector, 2nd and 3rd anoxic tanks, respectively (influent flow distribution before the anaerobic selector). The results for the entire experimental period showed high removal efficiencies of organic matter of 89% as total chemical oxygen demand removal and 95% removal for biochemical oxygen demand, 90% removal of total Kjeldahl nitrogen and total nitrogen removal through denitrification of 73%, mean phosphorus removal of 67%, as well as excellent settleability. The highest removal efficiency and the optimum performance were recorded at an HRT of about 9h and influent flow rate of 96 l d(-1), in which 60% is distributed to the anaerobic selector, 25% to the second anoxic tank and 15% to the last anoxic tank. Consequently, the plant configuration enhanced removal efficiency, optimized performance, saved energy, formed good settling sludge and provided operational assurance.

Biological removal of nitrogen from wastewater

This comprehensive review discusses diverse conventional and novel technologies for nitrogen removal from wastewater. Novel technologies have distinct advantages in terms of saving configuration, aeration, and carbon sources. Each novel technology possesses promising features and potential problems. For instance, SND and OLAND processes can achieve 100% total nitrogen removal, but the low oxygen concentration required by these two processes substantially reduces the nitrification rate, which limits their application. On the other hand, denitrification can still be carried out by aerobic denitrifiers at high DO levels in activated sludge process, but it is difficult to cultivate this type of bacteria. The SHARON process is most commonly used for shortcut nitrification and denitrification because of its low requirements for retention time, oxygen concentration, and carbon source. However, its high operational temperature (about 35 degrees C) limits the application. Several real-time control strategies (DO, pH, and ORP) have been developed to achieve a stable nitrite accumulation in SHARON. The ANAMMOX process can sustain at high total-N loadings and has been employed in full-scale treatment plants, but the problem of nitrite supply has not been solved, and the treated wastewater still contains nitrate. In addition, the inoculation and enrichment of ANAMMOX bacteria (i.e., anaerobic AOB) is difficult. The problem of nitrite supply has been solved by combining partial nitrification with ANAMMOX, which provides abundant nitrite for anaerobic AOB. ANAMMOX is currently used for treating sludge digestion supernatant. Aerobic dammonitrification is a process combining partial nitrification and ANAMMOX at different layers of biofilm. Although the technology has been tested in pilot- and full-scale experiments, the mechanism is still unclear. CANON and OLAND are one-step ammonium removal processes that possess distinct advantages of saving carbon sources and aeration costs. The major challenge is the enrichment of anaerobic microorganisms capable of oxidizing ammonia with nitrite as the electron acceptor. Molecular biology and environmental biotechnology can help identify functional microorganisms, characterize microbial communities, and develop new nitrogen removal processes. Extensive research should be conducted to apply and optimize these novel processes in wastewater treatment plants. More effort should be invested to combine these novel processes (e.g., partial nitrification, ANAMMOX) to enhance nitrogen removal efficiency.