A new sulfur bioconversion process development for energy- and space-efficient secondary wastewater treatment

This study evaluated startup strategies for mainstream polishing anammox moving bed biofilm reactors (MBBRs) without anammox bacterial (AMX) biomass inoculation. Two types of startups were tested: anammox only (no external carbon addition) and partial denitrification/anammox (PdNA) with glycerol addition. Reactors were started with either virgin carriers or carriers with a preliminary biofilm from a mainstream aerobic integrated fixed‐film activated sludge (IFAS) process. Three pilot‐scale startups were completed under the following conditions: anammox‐only with preliminary biofilm carriers, PdNA with preliminary biofilm carriers, and PdNA with virgin carriers. AMX presence was confirmed via quantitative polymerase chain reaction (qPCR) after 57, 57, and 77 days, respectively. Prior to AMX detection, average influent concentrations of ammonia and nitrite ranged from 1.7–2.7 mg/L and 0.98–1.8 mg/L, respectively. This study demonstrated that AMX can be grown on carriers without AMX seeding under mainstream conditions (temperature 17–29°C, low ammonia and nitrite), regardless of whether nitrite came from upstream or partial denitrification within the reactor. This study also showed that using preliminary biofilm carriers can decrease startup time by approximately 1 month. These results address critical questions for moving mainstream anammox processes to full‐scale implementation, and suggest that PdNA MBBRs are feasible and sustainable for full‐scale ammonia, nitrate, and nitrite polishing to meet stringent total nitrogen requirements.Practitioner Points This research will help utilities develop methods for starting up mainstream anammox MBBRs without the barrier of anammox biomass seeding. Preliminary biofilm carriers accelerated startup time in a PdNA MBBR, but a virgin carrier reactor started up in a similar timeframe, contrary to expectations. Also, contrary to expectations, high concentrations of ammonia and nitrite are not necessary for startup of an anammox or PdNA MBBR.

Salinity shock severely impairs the partial denitrification/anammox (PD/A) process, leading to prolonged functional deterioration and slow reactivation of anaerobic ammonium-oxidizing bacteria (anammox). To develop an effective strategy for mitigating salinity-induced inhibition, this study systematically examined the role of exogenous hydroxylamine (NH2OH) in accelerating PD/A recovery using short-term batch assays and long-term reactor operation. Hydroxylamine exhibited a clear concentration-dependent effect on system reactivation. In batch tests, low-dose hydroxylamine (10 mg/L) markedly enhanced anammox activity, increasing the ammonium oxidation rate to 5.5 mg N/(g VSS·h), representing a 42.5% increase, indicating its potential to stimulate key nitrogen-transforming pathways following salinity stress. During continuous operation, hydroxylamine at 5 mg/L proved optimal for restoring reactor performance, achieving stable nitrogen removal with 87% NH4+-N removal efficiency. The nitrite transformation ratio (NTR) reached approximately 80% within 13 cycles, 46 cycles ahead of the control, while simultaneously promoting the enrichment of key functional microbial taxa, including Thauera and Candidatus Brocadia. Hydroxylamine addition also triggered the production of tyrosine- and tryptophan-like proteins within extracellular polymeric substances, which enhanced protective and metabolic functionality during recovery. In contrast, a higher hydroxylamine dosage (10 mg/L) resulted in persistent NO2−-N accumulation, substantial suppression of Candidatus Brocadia (declining from 0.67% to 0.09%), and impaired system stability, highlighting a dose-sensitive threshold between stimulation and inhibition. Overall, this study demonstrates that controlled low-level hydroxylamine supplementation can effectively reactivate salinity-inhibited PD/A systems by enhancing nitrogen conversion, reshaping functional microbial communities, and reinforcing stress-response mechanisms. These findings provide mechanistic insight and practical guidance for improving the resilience and engineering application of PD/A processes treating saline wastewater.

Wastewater of municipal toilets contains higher nitrogen to carbon ratio than other types of wastewater. The removal of nitrogen from municipal toilet wastewater has become a major concern due to problems caused by discharge of insufficiently treated wastewater, such as eutrophication and toxicity. Moving Bed Biofilm Reactor (MBBR) has been developed in order to facilitate nitrogen removal. Treatment of nitrogen is commonly achieved in separate aerobic and anoxic tanks in typical MBBR systems. However the treatment process using a single MBBR tank as an advantageous method because of the low cost and low complexity, has not been thoroughly studied. This research is focused on the performance of MBBR in nitrogen removal based on simultaneous nitrification and de-nitrification in single aerobic MBBR with continuous operation. A moving-bed biofilm reactor system with an anoxic–aerobic arrangement was set up and the wastewater extracted from the wastewater treatment plant at temple of Tooth Relic, Kandy, was kept in the prepared laboratory set up for the accumulation of microorganisms. The operation was carried out in 3 steps. In the first step, the DO concentration in the reactor was maintained at 5 mg/l and the synthetic wastewater was introduced initially to the reactor at low nitrogen concentration. Then, the nitrogen concentration was increased varying the BOD/N. In the second step BOD/N ratio was maintained at 4.2, which is the BOD/N value of public toilet wastewater and the DO concentration was varied. Volatile Suspended Solids (VSS) of the reactor was kept at around 2200 mg/l. In the third step the DO concentration was maintained at 1.5 mg/l since it was the optimum DO concentration for highest de-nitrification in the 2nd step. Then the VSS of the reactor was maintained at 2200 mg/l and the BOD/N ratio was varied. Under the operating conditions, 67% of BOD and COD removal and 60% of TN removal could be achieved from the prepared laboratory set up. Further it was observed that the removal of nitrogen increased when the BOD/N ratio was increased.

For small wastewater treatment plants (WWPTs), high-rate secondary treatment systems with good treatment efficiency and easy, stable, and robust operation are called for. In this paper an experimental study on a high rate secondary treatment based on moving bed biofilm reactor (MBBR) and multimedia filters is presented. A high rate MBBR converts easily biodegradable SCOD in short HRT (0.5 h) directly after screening, then a Kaldnes-Filtralite-Sand (KFS) filter removes the particulate COD and detached biofilms at filtration rates of 10–20 m/h. The whole system gave effluent SS and COD less than 30 mg/L and 100 mg/L when total detention time is less than 1 h and small dosage of chemicals (iron and/or cationic polymer) is used. A new scenario of high rate secondary system with a primary Kaldnes coarse media filter in front of high rate MBBR and the KFS filter is proposed and discussed. This scenario with total HRT less than 2 h is more suitable for high influent SS concentrations and may also be extended for nitrogen and phosphorous removal. Compared to conventional secondary treatment, the high rate secondary treatment will be using only 1/5–1/10 of the space, resulting in considerable savings for construction, energy and operation.

Carbon-efficient Nutrients removal from real municipal wastewater under conditions of highly variable influent quality and low temperature

Deammonification, which is based on partial nitritation and anammox (PN/A), is a well-established sidestream treatment for nitrogen removal. However, transferring deammonification to mainstream wastewater treatment remains challenging due to low temperatures, the need to retain slow-growing anammox bacteria (AnAOB), and their competition for nitrite with nitrite-oxidizing bacteria (NOB) and heterotrophic denitrifiers. This work investigates cubic polyurethane foam carriers to promote growth and retention of AnAOB. A moving bed biofilm reactor (MBBR) and an integrated fixed-film activated sludge (IFAS) reactor were compared over a three-year experimental period at lab-scale. The feasibility of the biofilm carriers for deammonification was first evaluated under sidestream conditions, followed by a stepwise transition to mainstream operational conditions. The impact of operational parameters, including dissolved oxygen concentration, pH value, and aeration strategy, was evaluated with respect to the activity of aerobic ammonium-oxidizing bacteria (AOB), NOB, and AnAOB, as well as nitrogen removal rates. Deammonification reached nitrogen removal rates of 0.04–0.12 kg N m−3 d−1 (IFAS reactor) and 0.02–0.28 kg N m−3 d−1 (MBBR) at subphases with reactor bulk concentrations above 60 mg NH4-N L−1. Highest nitrogen removal degrees of 77 ± 6% (IFAS) and 76 ± 5% (MBBR) were achieved at reactor bulk concentrations of 96 mg NH4 L−1 and 97 mg NH4 L−1, respectively. Lower concentrations triggered NOB activity in both reactors, leading to an increase in nitrate concentration up to 22 mg NO3-N L−1. AOB and AnAOB activities were on average 6-fold higher on the carriers compared to suspended biomass throughout all experimental phases, demonstrating the feasibility of using cubic polyurethane foam carriers for deammonification. This was also confirmed by fluorescence in-situ hybridization (FISH) measurements. Median nitrogen removal rates over all experimental phases of 0.07 kg N m−3 d−1 for the IFAS reactor and 0.05 kg N m−3 d−1 for the MBBR were achieved, which are comparable to conventional activated sludge systems performing nitrogen removal via nitrification–denitrification. While at lower nitrogen concentrations, the IFAS reactor yielded superior nitrogen removal rates, peak nitrogen removal rates of 0.28 kg N m−3 d−1 were measured in the MBBR configuration. However, controlling NOB activity at lower temperatures and concentrations remains a challenge in MBBR and IFAS configurations. In our study, in the IFAS reactor NOB activities were visible on fewer days than in MBBR. At mainstream-like conditions, higher nitrogen removal rates of IFAS (0.09–0.12 kg N m−3 d−1) were achieved compared to the MBBR (0.06–0.09 kg N m−3 d−1). This demonstrates the advantage of the IFAS reactor in treating mainstream wastewater via deammonification. As an autotrophic nitrogen removal process, the implementation of deammonification in the mainstream of municipal wastewater treatment plants enables enhanced recovery of biogas from sewage organic matter. The latter would otherwise be consumed during the conventional nitrification-denitrification pathway. Consequently, the overall energy balance for wastewater treatment can be improved, contributing to a more environmentally sustainable process.

Stage by stage design for primary, conventional activated sludge, SBR and MBBR units for residential wastewater treatment and reusing

This study benchmarks vermifiltration (VF) as secondary wastewater treatment in three nature-based decentralized treatment plants using life-cycle assessment. The comparison is justified by the comparatively easier and cheaper operation of VF when compared to more traditional technologies, including small rate infiltration (SRI), constructed wetlands (CW), and activated sludge (AS). Standard life cycle assessment was used and applied to three case studies located in southern Europe. Material intensity during construction was highest for VF, but impacts during operation were lower, compensating those of the other phases. Impacts during the construction phase far outweigh those of operation and dismantling for facilities using constructed wetlands and activated sludge, when the number of served inhabitants is small, and due to lack of economies of scale. VF used as secondary treatment was shown to contribute to reducing the environmental impacts, mainly in constructed wetlands and activated sludge. The replacement of CW by VF seems to bring important environmental benefits in most impact categories, in particular in the construction phase. The replacement by VF in facilities with SRI seems to result in the improvement of some of the impact categories, in particular in the operation phase. As for dismantling, no conclusive results were obtained.

Simultaneous nitrogen and carbon removal from wastewater at different operating conditions in a moving bed biofilm reactor (MBBR): Process modeling and optimization

Manganese (Mn) is a difficult metal to remove in acid mine drainage because of high pH requirements for oxidation of Mn to form Mn oxide precipitates. However, Mn removal can be quickened in a gravel system providing a large surface area and high pH for Mn oxidation to occur with microbiological mediation. An experiment was designed with 12 gravel bed mesocosms that were 9.8 m3 × 6.7 m3 × 0.6 m3 to determine the best design criteria for optimizing Mn removal. Treatments consisted of two Mn loading rates (1.1 and 2.7 g/m2·d) and two gravel types (limestone and river gravel) and were replicated three times. Water flowed through the experimental wetlands for 734 days. Manganese removal was more effective in limestone than in river gravel. Manganese removal was not affected by water temperature ranging from 5 to 30 °C in either rock material. Manganese removal rates ranged from 100 to 600 m/a in the limestone wetlands and 10 to 60 m/a in the river gravel wetlands. Greater pH in limestone (approximately 6.9) compared with river gravel (approximately 5.5) favored Mn oxide precipitation. Greater pH, coupled with oxidation–reduction potential (redox) values greater than 430 mV in the limestone, resulted in water chemistry near conditions predicting manganite to be the dominant Mn phase. Ideal pH and redox conditions for Mn removal are pH from 6.8 to 7.2 and redox greater than 500 mV. The range of dissolved oxygen (DO) required to remove Mn in the various wetlands ranged from 3 to 5 mg/L, with approximately one‐half of the DO loss caused by Mn hydroxide formation and one‐half ascribed to biological consumption. The influent DO should be at least 0.35 mg/L for every 1 mg/L Mn removed. Removal rates for Mn ranged from 1 to 17 g/m2·d in limestone and from 1 to 2 g/m2·d in river gravel. Limestone is the material of choice for subsurface flow wetlands for Mn removal. Removal rates and required chemistry determined in this study can be used to design subsurface flow wetlands for optimum Mn removal.

Robust PD/A biofilms sustain advanced real municipal wastewater treatment: Reinforcement of interspecific communication and electron transfer

Performance of three different structures of moving bed biofilm reactors (MBBR) treating synthetic wastewater was evaluated. The three systems were operated under the same conditions of dissolved oxygen (DO) 3 mg/L at 26 °C. The effluent of chemical oxygen demand (COD) decreased from 111.6 mg/L in reactor 1 (R1), 128.8 mg/L in reactor 2 (R2), and 154.5 mg/L in reactor 3 (R3), to less than 100 mg/L, respectively, with concentration of influent NH4+-N rising from 30 mg/L to 50 mg/L. The concentration of effluent NH4+-N for R1, R2 and R3 were close to 2 mg/L, 4 mg/L and 5 mg/L, respectively. The highest TN removal rate in R1 achieved average 84.4 %, which was 6.0 % and 9.7 % higher than those of R2 and R3, respectively. R1 with two baffles in it exhibited well fluidization and abundant microbes growing on carrier.

The concentrations of Escherichia coli, F-specific RNA bacteriophage (FRNA bacteriophage), and norovirus genogroup I (NoV GI) and norovirus genogroup II (NoV GII) in wastewater were monitored weekly over a 1-year period at a wastewater treatment plant (WWTP) providing secondary wastewater treatment. A total of 49 samples of influent wastewater and wastewater that had been treated by primary and secondary wastewater treatment processes (primary and secondary treated wastewater) were analyzed. Using a real-time reverse transcription-quantitative PCR (RT-qPCR), the mean NoV GI and NoV GII concentrations detected in effluent wastewater were 2.53 and 2.63 log(10) virus genome copies 100 ml(-1), respectively. The mean NoV concentrations in wastewater during the winter period (January to March) (n = 12) were 0.82 (NoV GI) and 1.41 (NoV GII) log units greater than the mean concentrations for the rest of the year (n = 37). The mean reductions of NoV GI and GII during treatment were 0.80 and 0.92 log units, respectively, with no significant difference detected in the extent of NoV reductions due to season. No seasonal trend was detected in the concentrations of E. coli or FRNA bacteriophage in wastewater influent and showed mean reductions of 1.49 and 2.13 log units, respectively. Mean concentrations of 3.56 and 3.72 log(10) virus genome copies 100 ml(-1) for NoV GI and GII, respectively, were detected in oysters sampled adjacent to the WWTP discharge. A strong seasonal trend was observed, and the concentrations of NoV GI and GII detected in oysters were correlated with concentrations detected in the wastewater effluent. No seasonal difference was detected in concentrations of E. coli or FRNA bacteriophage detected in oysters.

Low-dose chlorite drives stable nitrite accumulation for partial denitrification.

Integrated biological sulfidogenic process: Synergizing sulfate and elemental sulfur reduction for metal-laden wastewater treatment.