Reducing excess sludge volume in sequencing batch reactor by integrating ultrasonic waves and ozonation

The effects of ultrasonic waves and ozonation on the reduction of produced sludge in the sequencing batch reactor (SBR) system were investigated in laboratory-scale experiments. For this purpose, the optimal ozone dosage was determined by measuring soluble chemical oxygen demand (SCOD), protein concentration, turbidity level, and biomass yield coefficient. Next, the effect of its integration with different levels of ultrasonic specific energy was evaluated. Based on the results, the minimum excess sludge production in the SBR system was achieved at the ozone dosage of 11 mg O₃/g MLSS followed by ultrasonic specific energy of 12000 kJ/kg TS. In this case, the biomass yield coefficient decreased from 0.75 in the control reactor to 0.34 mg MLSS/mg COD in the test reactor, which was equal to a 54% reduction in excess sludge production in the SBR system. In these circumstances, the removal efficiencies of COD, total nitrogen, and total phosphorus were measured as 90%, 82%, and 81%, respectively.

Enhancement of nitrogen and phosphorus removal, sludge reduction and microbial community structure in an anaerobic/anoxic/oxic process coupled with composite ferrate solution disintegration

Waste activated sludge (WAS) was disintegrated by composite ferrate solution (CFS) in this work, and the effect of CFS disintegrated sludge supernatant (CDSS), as a supplementary carbon source, on enhancement of nitrogen and phosphorus removal and sludge reduction in an AAO-CFSSDR (Anaerobic/Anoxic/Oxic combined with CFS-Sludge disintegration reactor) process was evaluated. The results showed that CDSS was easily utilizable by the denitrification bacteria due to the high content of readily biodegradable substrates. When compared with the AAO process, the operation results of AAO-CFSSDR suggested that the removal efficiencies of TN, NH₄⁺-N and TP increased from 71.15, 79.23 and 85.52% to 85.05, 87.70 and 90.06%, respectively; and the sludge was reduced by 34.79%. The 16SrRNA high-throughput sequencing results showed that the introduction of CDSS weakened the microbial diversity but enhanced the microbial richness; and the abundance of bacteria related to the removal of nitrogen and phosphorus, increased in the AAO-CFSSDR process.

Responses of microbial structures, functions, metabolic pathways and community interactions to different C/N ratios in aerobic nitrification

The responses of microbial structures, functional profiles and metabolic pathways during nitrification to four C/N ratios (0, 5, 10 and 15) were investigated in four parallel SBRs denoted as S₀, S₅, S₁₀, S₁₅. Results indicated that microbial diversities were affected by C/N ratios, while the same dominant taxa were observed, mainly including Proteobacteria, Betaproteobacteria, Rhodocyclales, Rhodocyclaceae, Zoogloea. The unique biomarkers were identified in each sludge sample through LEfSe analysis. Functional genera/enzymes responsible for removing organics and nitrogen coexisted in four SBRs at different abundances, except for that ammonia oxidizing bacteria (AOB) Nitrosomonas (0.33%-0.66%) and ammonia monooxygenase (amo) (9.4 × 10^-7-2.8 × 10^-6) were only detected in S₀. Moreover, PICRUSt analysis indicated similar overall patterns of metabolic pathways in four sludge samples. The network analysis revealed that total nitrogen removal positively correlated with hcp (Spearman's ρ of 0.853), and ammonia oxidizing rate was associated with amo (Spearman's ρ of 0.096).

Temperature effect on extracellular polymeric substances (EPS) and phosphorus accumulating organisms (PAOs) for phosphorus release of anaerobic sludge

Phosphorus (P) is an essential element for living organisms and anaerobic sludge is an attractive source for P recovery. Anaerobic P release depends on both phosphorus-accumulating organisms (PAOs) and extracellular polymeric substances (EPS). However, the P release contributed by the microbial cells and EPS was not addressed completely and the effect of temperature on the mechanism of P release and transformation was rarely considered. This study, therefore, investigated the effects of temperature on the P fraction and the relationship between PAOs metabolic pathway and EPS reaction using the Standards in Measurements and Testing (SMT) protocol and the ³¹P nuclear magnetic resonance (³¹P-NMR) experiments. Experimental results showed that the temperature not only affected the metabolism of PAOs, but also significantly influenced the EPS components and the hydrolysis of EPS-associated polyphosphate (poly-P). And the P release mainly occurred due to biological mechanisms with a conversion from non-reactive P (NRP) in both intracellular and extracellular substances to reactive P (RP) fractions. The highest concentration of total P in the supernatant (TP_L) occurred at 15 °C, and the TP_L release from the solid to liquid phase was better fitted with pseudo-second-order kinetic model. More organic P in the sludge (OP_s) released from the sludge phase at 35 °C would convert into inorganic P (IP_s) and non-apatite inorganic phosphorus (NAIP_s) was the most labile P fraction for P release. The hydrolysis of EPS-associated poly-P was enhanced by higher temperatures with the degradation of the long-chain poly-P by PAOs. Meanwhile, a lower temperature could obviously improve the P release because the dominance of PAOs would potentially shift to GAOs with the increase of temperature. But the very-low temperature (5 °C) was not beneficial for the P release and suppressed the microbial activities.

Phosphorus (P) is an essential element for living organisms and anaerobic sludge is an attractive source for P recovery.

Efficiency, granulation, and bacterial populations related to pollutant removal in an upflow microaerobic sludge reactor treating wastewater with low COD/TN ratio

In this study, a novel upflow microaerobic sludge reactor (UMSR) was constructed to conduct anaerobic digestion of municipal wastewater with low carbon and nitrogen ratio (C/N). Oxygen in the UMSR was supplied by falling water and external recirculation. Excellent nitrogen removal performance was obtained in the UMSR for treating wastewater with low C/N ratio at a temperature of 25 °C and a hydraulic retention time of 24 h. Ammonium and total nitrogen removal efficiencies averaged 92.35% and 90.41%, respectively, and sludge granulation occurred during acclimation. The inferred metabolism of nitrogen removal and ecological positions of functional microbe were integrated into a granule model by scanning electron microscopy. Additionally, the analysis of microbial community indicated that aerobic nitrifying bacteria and heterotrophic bacteria survived on the surface of sludge floc and granules while the anaerobic autotrophic, heterotrophic denitrifying, and anaerobic ammonia oxidation bacteria were present in the inner layer.

Enhanced nitrogen removal from piggery wastewater with high NH4+ and low COD/TN ratio in a novel upflow microaerobic biofilm reactor

To enhance nutrient removal more cost-efficiently in microaerobic process treating piggery wastewater characterized by high ammonium (NH₄⁺-N) and low chemical oxygen demand (COD) to total nitrogen (TN) ratio, a novel upflow microaerobic biofilm reactor (UMBR) was constructed and the efficiency in nutrient removal was evaluated with various influent COD/TN ratios and reflux ratios. The results showed that the biofilm on the carriers had increased the biomass in the UMBR and enhanced the enrichment of slow-growth-rate bacteria such as nitrifiers, denitrifiers and anammox bacteria. The packed bed allowed the microaerobic biofilm process perform well at a low reflux ratio of 35 with a NH₄⁺-N and TN removal as high as 93.1% and 89.9%, respectively. Compared with the previously developed upflow microaerobic sludge reactor, the UMBR had not changed the dominant anammox approach to nitrogen removal, but was more cost-efficiently in treating organic wastewater with high NH₄⁺-N and low COD/TN ratio.

Effect of reflux ratio on nitrogen removal in a novel upflow microaerobic sludge reactor treating piggery wastewater with high ammonium and low COD/TN ratio: Efficiency and quantitative molecular mechanism

A novel upflow microaerobic sludge reactor (UMSR) was constructed to treat manure-free piggery wastewater with high NH₄⁺-N and low COD/TN ratio. In the light of the potential effect of effluent reflux ratio (RR) on nitrogen removal, performance of the UMSR was evaluated at 35°C and hydraulic retention time 8h with RR decreased from 45 to 25 by stages. A COD, NH₄⁺-N and TN removal of above 77.1%, 80.0% and 86.6%, respectively, was kept with a RR over 35. To get an effluent of TN not more than 80mg/L with a TN load removal above 0.88kg/(m³·d), the RR should be at least 34. Real-time quantitative polymerase chain reaction of functional bacteria revealed that the RR of less than 34 stimulated ammonium oxidation but badly inhibited anammox, the dominant nitrogen removal pathway, resulting in the remarkable decrease of nitrogen removal in the reactor.

Enhanced phosphorus removal in intermittently aerated constructed wetlands filled with various construction wastes

Phosphorus (P) loss by various pathways in constructed wetlands (CWs) is often variable. The effects of intermittent aeration and different construction waste substrates (gravel, red brick, fly-ash brick) on P processing using six batch-operated vertical flow constructed wetlands (VFCWs) were studied for decentralized domestic wastewater treatment. Average removal of total phosphorus (TP) in three aerated CWs was markedly higher (21.06, 24.83, and 27.02 mg m^-2 day^-1, respectively) than non-aerated CWs (10.64, 18.16, and 25.09 mg m^-2 day^-1, respectively). Fly-ash brick offered superior TP removal efficiency in both aerated and non-aerated batch-operated VFCWs, suggesting its promising application for P removal in CWs. Aeration greatly promoted plant growth and thusly increased plant uptake of P by 0.57-1.45 times. Substance storage was still the main P sink accounting for 23.92-59.47% of TP removal. Other process including microbial uptake was revealed to be a very important P removal pathway (accounting for 14.86-34.84%). The contribution of microbial uptake was also indicated by microbial analysis. Long-term results suggested that the contribution of microbial P uptake could be always ignored and underestimated in most CWs. A combination of intermittent aeration and suitable substrates is effective to intensify P transformation in CWs.

SRT contributes significantly to sludge reduction in the OSA-based activated sludge process

Though activated sludge systems have contributed significantly to the control of hygiene of our society, the wastewater treatment generates large amount of excess sludge. The oxic-settling-anaerobic (OSA)-based biological processes have been shown to be promising approaches for sludge reduction during wastewater treatment. However, the sludge reduction mechanism is still unclear. Four conditions were examined to clarify the sludge reduction mechanism in the OSA-based process. Sludge retention time (SRT) was the main 'contributor' to sludge reduction. The sludge reduction percentage of the process with side hydrolysis and acidification was 42%, with the contribution by long SRT of 33%, energy uncoupling of 7.7%, and hydrolysis/acidification of 1.1%. In addition, the sludge reduction in the OSA-based process had no obvious impact on the efficiency of nutrient removal. The clarified mechanism for sludge reduction in the OSA-based process could provide valuable clue for future system optimization.

Effect of seed sludge on nitrogen removal in a novel upflow microaerobic sludge reactor for treating piggery wastewater

Anaerobic activated sludge (AnaS) and aerobic activated sludge (AerS) were used to start up a novel upflow microaerobic sludge reactor (UMSR), respectively, and the nitrogen removal in the two reactors were evaluated when treating low C/N ratio manure-free piggery wastewater with a COD/TN ration of about 0.85. With the same hydraulic retention time 8h and TN loading rate (NLR) 0.42kg/(m(3)d), the UMSR (R2) inoculated with AerS could reach its steady state earlier and obtained a better TN removal than that in the UMSR (R1) inoculated with AnaS. However, the accumulated AnaS made R1 show a better capability in bearing shock load and demonstrated an excellent NH4(+)-N and TN removal with a NLR as high as 1.07kg/(m(3)d). Microbial community structure of the accumulated AerS and AnaS were observable different. The decreased proportion of nitrifiers restricted the ammonium oxidation in R2, and resulting in a decrease in TN removal.

The effect and biological mechanism of COD/TN ratio on nitrogen removal in a novel upflow microaerobic sludge reactor treating manure-free piggery wastewater

A novel upflow microaerobic sludge reactor (UMSR) was constructed to treat manure-free piggery wastewater with high NH4(+)-N concentration and low COD/TN ratio, and the effect and biological mechanism of COD/TN ratio on nitrogen removal were investigated at a constant hydraulic retention time of 8h and 35°C. The results showed that the UMSR could treat the wastewater with a better synchronous removal of COD, NH4(+)-N and TN. The microaerobic UMSR allowed nitrifiers, and heterotrophic and autotrophic denitrifiers to thrive in the flocs, revealing a multiple nitrogen removal mechanism in the reactor. Both the nitrifiers and denitrifiers would be restricted by an influent COD/TN ratio more than 0.82, resulting in a decrease of TN removal in the UMSR. To get a TN removal over 80% with a TN load removal above 0.86kg/(m(3)·d) in the UMSR, the influent COD/TN ratio should be less than 0.70.

Development of an integrated system for the treatment of rural domestic wastewater: emphasis on nutrient removal

A novel, integrated treatment system consisting of a multi-stage bio-filter and a post positioned denitrifying bio-reactor was designed and developed in this study for the treatment of rural domestic wastewater emphasizing on nutrient removal.

Efficient and microbial communities for pollutant removal in a distributed-inflow biological reactor (DBR) for treating piggery wastewater

To treat piggery wastewater with a low C/N ratio, a novel distributed-inflow biological reactor (DBR) was developed that assures the proper organic flow for an efficient denitrification process.

Simultaneous in-situ sludge reduction and nutrient removal in an A(2)MO-M system: Performances, mechanisms, and modeling with an extended ASM2d model

Among the existing in-situ sludge reduction processes, the oxic-settling-anaerobic (OSA) process is of particular interest because it has shown significant sludge reduction with several advantages. However, an ideal process for practical application must simultaneously incorporate effluent quality with sludge reduction. In this study, an improved OSA system, the stage-aerated anaerobic, anoxic, micro-aerobic, and oxic system combining a micro-aerobic starvation tank (abbreviated as A(2)MO-M system) was developed. Compared with OSA3# (hydraulic retention time (HRT) of 12 h), the A(2)MO-M2# system with optimized HRT of 9 h yielded almost 16.3% less sludge. The average total nitrogen (87.3%) and total phosphorus (91.9%) removal efficiencies in A(2)MO-M2# were 20.6 and 42.2% higher than those in OSA3#. Investigation of the mechanisms of sludge reduction revealed that, except for the main factors of energy uncoupling metabolism (16.7%) and sludge decay (21.2%), enrichment of slow-growing bacteria and lysis-cryptic growth metabolism analyzed by high-throughput 454 pyrosequencing were shown to contribute to sludge reduction in the A(2)MO-M system. On the basis of effluent organic matters (EfOM) measurements, soluble microbial products (SMP) were the major components in EfOM; and different reduction-oxidation (redox) potentials controlled in the OSA and A(2)MO-M systems led to different SMP formation mechanisms. To explore the mechanism and kinetics of SMP formation under different redox potentials, three new components (SUAP, SBAP, and XEPS) were integrated in an extended ASM2d model. Experimental and modeling results revealed that biomass-associated products (BAP) supported a substantial population of SMP that were quite sensitive to different redox potentials. The extended ASM2d model further illustrated that more BAP produced in the alternating anaerobic and aerobic conditions in the OSA system adversely affected its effluent quality.

Performance and characterization of a non-sintered zeolite porous filter for the simultaneous removal of nitrogen and phosphorus in a biological aerated filter (BAF)

A novel non-sintered zeolite porous filter (ZPF) and commercially available ceramsite (CAC) are used to investigate the simultaneous removal of nitrogen and phosphorus from city wastewater treated by biological aerated filter (BAF) reactors.

Combination of ultrasound and Fenton treatment for improving the hydrolysis and acidification of waste activated sludge

US/Fenton had a synergetic effect on improving the hydrolysis and subsequent acidification of WAS.