Treatment performance and N2O emission in the UASB-A/O shortcut biological nitrogen removal system for landfill leachate at different salinity

Nitrous Oxide Emissions from Nitritation Reactors under Hypersaline Conditions

This study focuses on nitrous oxide (N2O) emissions during hypersaline (4 % salinity) nitritation in continuously fed and mixed fixed bed reactors. In the presence of high concentrations of nitrite and ammonium, the percent yield of N2O emissions from ammonium removed decreased with increasing dissolved oxygen (DO). However, N2O production continued even at a high DO of 15 mg/L. Bulk ammonium concentration (not ammonia) was found to be the main controlling factor for N2O emissions under high and low DO during both nitritation and nitrification. Reducing bulk ammonium concentrations below 1 mg N/L in the nitritation reactor under both high and low DO conditions resulted in a reduction of N2O emissions of approximately 90 %. Under full nitrification and low DO, reducing nitrite concentrations below 0.3 mg N/L resulted in a 60 % reduction in N2O emissions. Similar results were observed in a low salinity reactor.

Microbial mechanisms of refractory organics degradation in old landfill leachate by a combined process of UASB-A/O-USSB

A combined process of anaerobic digestion (UASB), shortcut nitrification-denitrification (A/O), and semi-anoxic co-metabolism (operated by an up-flow semi-anoxic sludge bed; USSB) was constructed for the treatment of old landfill leachate (>10 years). The performance and mechanism of refractory organics degradation by the combined process (UASB-A/O-USSB) were investigated. The results showed that the semi-anoxic co-metabolism contributes 57 % of the totally degraded refractory organics. Specific microorganisms and their corresponding metabolic functions drive the degradation of refractory organics in each unit of the UASB-A/O-USSB process. In detail, organics with simple molecular structures were preferentially degraded by anaerobic digestion and shortcut denitrification, whereas those with complex structures were subsequently degraded in the oxic tanks and USSB reactor by shortcut nitrification and semi-anoxic co-metabolism. The structural equation model showed that the combined process of shortcut nitrification and semi-anoxic co-metabolism had a better effect on the degradation of recalcitrant organics than the single process. These findings provide information on how refractory organics are metabolically degraded in a combined process.

Can anammox process be adopted for treating wastewater with high salinity exposure risk?

Anammox was a promising technology for nitrogen removal, and has been applied for treating many kinds of nitrogenous wastewaters. Considering the risk in high salinity of the municipal sewage in coastal city, the feasibility of Anammox process for treating low ammonia wastewater (around 50 mg L^-1) with increasing salinity was investigated in this study. The results showed that the salinity in low concentrations (1-5 g L^-1) had slight impact on the nitrogen removal and activity of Anammox bacteria but significantly improved its growth. The moderate salinity (10-40 g L^-1) decreased the specific Anammox activity (SAA) to 8.11 from the initial 13.15 mg N g^-1 SS h^-1, but increased the abundance to 52.3% from 30.1% (Candidatus Kuenenia). High salinity (50-60 g L^-1) performed severe inhibition on activity and abundance both, with the SAA decreased to 0 and abundance to 11.9%. The self-recovery performance was unsatisfactory when salinity was unavailable. A quadratic curve between the SAA and salinity concentration was fitted, and the IC₅₀ was calculated as 42.1 g L^-1 (NaCl). Anammox process could be directly adopted for treating low ammonia sewage with low salinity, whereas activity enhancement or adaption improvement should be pre-presented for treating sewage with moderate or high salinity.

Nitrogen Removal from Mature Landfill Leachate via Anammox Based Processes: A Review

Mature landfill leachate is a complex and highly polluted effluent with a large amount of ammonia nitrogen, toxic components and low biodegradability. Its COD/N and BOD5/COD ratios are low, which is not suitable for traditional nitrification and denitrification processes. Anaerobic ammonia oxidation (anammox) is an innovative biological denitrification process, relying on anammox bacteria to form stable biofilms or granules. It has been extensively used in nitrogen removal of mature landfill leachate due to its high efficiency, low cost and sludge yield. This paper reviewed recent advances of anammox based processes for mature landfill leachate treatment. The state of the art anammox process for mature landfill leachate is systematically described, mainly including partial nitrification–anammox, partial nitrification–anammox coupled denitrification. At the same time, the microbiological analysis of the process operation was given. Anaerobic ammonium oxidation (anammox) has the merit of saving the carbon source and aeration energy, while its practical application is mainly limited by an unstable influent condition, operational control and seasonal temperature variation. To improve process efficiency, it is suggested to develop some novel denitrification processes coupled with anammox to reduce the inhibition of anammox bacteria by mature landfill leachate, and to find cheap new carbon sources (methane, waste fruits) to improve the biological denitrification efficiency of the anammox system.

Optimization of mixing ratio, shaking speed, contact time, and pH on reduction of Chemical Oxygen Demand (COD) and Ammoniacal Nitrogen (NH3-N) in leachate treatment

When the inevitable generation of waste is considered as hazardous to health, damaging ecosystem to our environment, it is important to develop an innovative technologies to remediate pollutant sources for the safety and environmental protection. The development of adsorption technique for the reduction of extremely effective pollutants in this regard. Green mussel and zeolite mixing media were investigated for the reduction of the concentration of organic constituents (COD) and ammoniacal nitrogen from leachate. The leachate treatability was analyzed under various stages of treatment parameter, namely mixing ratio, shaking speed, contact time, and pH. Both adsorbent were sieve values in between 2.00-3.35 mm particle size. The optimum pH, shaking speed, contact time, and mixing ratio were determined. Leachate samples were collected from influent untreated detention pond at Simpang Renggam landfill site in Johor, Malaysia. The result of leachate characterization properties revealed that non-biodegradability leachate with higher concentrations of COD (1829 mg/L), ammoniacal nitrogen (406.68 mg/L) and biodegradability value (0.08) respectively. The optimal reduction condition of COD and ammoniacal nitrogen was obtained at 200 rpm shaken speed, 120 minute shaken time, optimum green mussel and zeolite mix ratio was 2.0:2.0, and pH 7. The isothermic study of adsorption shows that Langmuir is best suited for experimental results in terms of Freundlich model. The mixing media also provided promising results to treating leachate. This would be greatly applicable in conventionally minimizing zeolite use and thereby lowering the operating cost of leachate treatment.Implications: The concentration of organic constituents (COD) and ammoniacal nitrogen in stabilized landfill leachate have significant strong influences of human health and environmental. The combination of mixing media green mussel and zeolite adsorbent COD and ammoniacal nitrogen reduction efficiency from leachate. This would be greatly applicable in future research era as well as conventionally minimizing high cost materials like zeolite use and thereby lowering the operating cost of leachate treatment.

Application of membrane separation technology in the treatment of leachate in China: A review

To comprehensively investigate the application of membrane separation technology in the treatment of landfill leachate in China, the performance of nearly 200 waste management enterprises of different sizes in China were analyzed, with an emphasis on their scale, regional features, processes, and economic characteristics. It was found that membrane separation technologies, mainly nanofiltration (NF), reverse osmosis (RO), and NF + RO, have been used in China since 2004. The treatment capacity of the two most dominant membrane separation technologies, i.e., NF and RO, were both almost 60,000 m³/d in 2018, and both technologies are widely used in landfills and incineration plants. Their distribution is mainly concentrated in eastern and southwestern China, where the amount of municipal solid waste (MSW) is relatively high and the economy is developing rapidly. Membrane separation technology is the preferred technique for the advanced treatment of leachate because more contaminants can be effectively removed by the technology than by other advanced processes. However, the membrane retentate that is produced using this technology-commonly known as leachate concentrate-is heavily contaminated due to the enrichment of almost all the inorganic anions, heavy metals, and organic matter that remain after bioprocessing. An economic cost analysis revealed that the operating cost of membrane separation technology has stabilized and is between 1.77 USD/m³ and 4.90 USD/m³; electricity consumption is the most expensive cost component. This review describes the current problems with the use of membrane separation technology and recommends strategies and solutions for its future use.

Transcriptional and metabolic response against hydroxyethane-(1,1-bisphosphonic acid) on bacterial denitrification by a halophilic Pannonibacter sp. strain DN

Biological denitrification is an environmentally sound pathway for the elimination of nitrogen pollution in wastewater treatment. Extreme environmental conditions, such as the co-existence of toxic organic pollutants, can affect biological denitrification. However, the potential underlying mechanism remains largely unexplored. Herein, the effect of a model pollutant, hydroxyethane-(1,1-bisphosphonic acid) (HEDP), a widely applied and consumed bisphosphonate, on microbial denitrification was investigated by exploring the metabolic and transcriptional responses of an isolated denitrifier, Pannonibacter sp. strain DN. Results showed that nitrate removal efficiency decreased from 85% to 50% with an increase in HEDP concentration from 0 to 3.5 mM, leading to nitrite accumulation of 204 mg L^-1 in 3.5 mM HEDP. This result was due to the lower bacterial population count and reduction in the live cell percentage. Further investigation revealed that HEDP caused a decrease in membrane potential from 0.080 ± 0.005 to 0.020 ± 0.002 with the increase in HEDP from 0 to 3.5 mM. This hindered electron transfer, which is required for nitrate transformation into nitrogen gas. Moreover, transcriptional profiling indicated that HEDP enhanced the genes involved in ROS (O₂^-) scavenging, thus protecting cells against oxidative stress damage. However, the suppression of genes responsible for the production of NADH/FADH₂ in tricarboxylic acid cycle (TCA), NADH catalyzation (NADH dehydrogenase) in (electron transport chain) ETC system and denitrifying genes, especially nor and nir, in response to 2.5 mM HEDP were identified as the key factor inhibiting transfer of electron from TCA cycle to denitrifying enzymes through ETC system.

Advanced nitrogen removal from mature landfill leachate via partial nitrification-Anammox biofilm reactor (PNABR) driven by high dissolved oxygen (DO): Protection mechanism of aerobic biofilm

A novel partial nitrification-Anammox biofilm reactor (PNABR) operated under high dissolved oxygen (DO) with pre-anoxic - aerobic - anoxic operational mode was developed for efficient denitrogenation from mature landfill leachate. With DO concentration gradually increasing to 4.03 ± 0.03 mg/L, the ammonia oxidation rate (AOR) was enhanced to 25.8 mgNH4+-N/(L h), while nitrite oxidation bacteria (NOB) was inhibited effectively by alternating free ammonia (FA) and oxygen starvation. DO micro-distribution revealed that estimated 1900 μm of aerobic biofilm could protect anammox biofilm underneath from being inhibited by high DO. qPCR analysis further suggested that ammonia oxidation bacteria (AOB) abundance in whole biofilm was 6.12 × 109 gene copies/(g dry sludge), which was twice than found in the floc. Anammox bacteria accounted for 2.39% of total bacteria in whole biofilm, contributing 90.0% to nitrogen removal. Nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) finally reached 396.6 gN/(m3 d) and 96.1%, respectively.

New insights into pollutants removal, toxicity reduction and microbial profiles in a lab-scale IC-A/O-membrane reactor system for paper wastewater reclamation

In this study, an internal circulation-anoxic/aerobic (IC-A/O) process followed by ultrafiltration (UF) and reverse osmosis (RO) system was applied for paper wastewater reclamation. The IC-AO system presented a stable and efficient performance, achieving high removal of chemical oxygen demand (COD), total organic carbon (TOC) and total nitrogen (TN) with methane production rate of 132.8 mL/d. Acute toxicity to Daphnia magna (D. magna) was reduced significantly (83.2%) and the spearman's rank correlation analysis indicated that the toxicity of effluents from each reactor were positively correlated with COD and TOC. Hexadecanoic acid, octadecanoic acid and benzophenone were the main toxic contributors for biological effluent. Microbial community revealed that Anaerolinea was significantly related with organic pollutants. The UF-RO system further removed pollutants and toxicity with the final effluent COD, TOC, ammonium nitrogen (NH₄⁺-N) and TN of 32.6, 18.8, 0.3 and 9.2 mg/L, respectively, which proved that it was feasible for paper wastewater reuse. This study presented an efficient, practical and environmentally competitive system, and paved a foundation for the treatment and reuse of paper wastewater.

Nitrogen removal in domestic wastewater. Effect of nitrate recycling and COD/N ratio

A denitrification/nitrification pilot plant was designed, built and put into operation, treating the effluent of an anaerobic reactor. The operation of the plant examined the effect of the nitrate recycling and the COD/N ratio on the nitrogen and the remaining organic matter removal at 18 °C. The system consisted of a two-stage treatment process: anoxic and aerobic. The hydraulic retention time (HRT) of the system was 1 h for the anoxic bioreactor and 2 h for the aerobic one. The increase in the nitrate recycling ratio did not cause a significant improvement in the nitrogen removal due to the insufficient carbon source. The wastewater to be treated had a C/N ratio of 1.1 showing a lack of organic carbon. The addition of methanol was a key point in the denitrification process used as a model for the traditional wastewater by-pass in the WWTP. The maximum nitrogen and organic matter removal (87.1% and 96%, respectively) was achieved with a nitrate recycling ratio of 600% and a C/N of 8.25, adjusted by methanol addition.

Optimal reduction of chemical oxygen demand and NH3-N from landfill leachate using a strongly resistant novel Bacillus salmalaya strain

Background

When the unavoidable waste generation is considered as damaging to our environment, it becomes crucial to develop a sustainable technology to remediate the pollutant source towards an environmental protection and safety. The development of a bioengineering technology for highly efficient pollutant removal is this regard. Given the high ammonia nitrogen content and chemical oxygen demand of landfill leachate, Bacillus salmalaya strain 139SI, a novel resident strain microbe that can survive in high ammonia nitrogen concentrations, was investigated for the bioremoval of ammonia nitrogen from landfill leachate. The treatability of landfill leachate was evaluated under different treatment parameters, such as temperature, inoculum dosage, and pH.

Results

Results demonstrated that bioaugmentation with the novel strain can potentially improve the biodegradability of landfill leachate. B. salmalaya strain 139SI showed high potential to enhance biological treatment given its maximum NH₃–N and COD removal efficiencies. The response surface plot pattern indicated that within 11 days and under optimum conditions (10% v/v inoculant, pH 6, and 35 °C), B. salmalaya strain139SI removed 78% of ammonia nitrogen. At the end of the study, biological and chemical oxygen demands remarkably decreased by 88% and 91.4%, respectively. Scanning electron microscopy images revealed that ammonia ions covered the cell surface of B. salmalaya strain139SI.

Conclusions

Therefore, novel resistant Bacillus salmalaya strain139SI significantly reduces the chemical oxygen demand and NH₃–N content of landfill leachate.

Graphical abstract

Leachate treatment by B. salmalaya strain 139SI within 11 days.

Leachate treatment in landfills is a significant N2O source

The importance of methane (CH₄) emissions from landfills has been extensively documented, while the nitrous oxide (N₂O) emissions from landfills are considered negligible. In this study, three landfills were selected to measure CH₄ and N₂O emissions using the static chamber method. Dongbu (DB) and Dongfu (DF) landfills, both located in Xiamen city, Fujian Province, were classified as sanitary. The former started to receive solid waste from Xiamen city in 2009, and the latter was closed in 2009. Nanjing (NJ) landfill, located in Nanjing county, Fujian Province, was classified as managed. Results showed that for the landfill reservoirs, CH₄ emissions were significant, while N₂O emissions occurred mainly in operating areas (on average, 16.3 and 19.0mgN₂Om^-2h^-1 for DB and NJ landfills, respectively) and made a negligible contribution to the total greenhouse gas emissions in term of CO₂ equivalent. However, significant N₂O emissions were observed in the leachate treatment systems of sanitary landfills and contributed 72.8% and 45.6% of total emissions in term of CO₂ equivalent in DB and DF landfills, respectively. The N₂O emission factor (EF) of the leachate treatment systems was in the range of 8.9-11.9% of the removed nitrogen. The total N₂O emissions from the leachate treatment systems of landfills in Xiamen city were estimated to be as high as 8.55gN₂O-Ncapita^-1yr^-1. These results indicated that N₂O emissions from leachate treatment systems of sanitary landfills were not negligible and should be included in national and/or local inventories of greenhouse gas emissions.

Nitrous oxide emissions in a membrane bioreactor treating saline wastewater contaminated by hydrocarbons

The joint effect of wastewater salinity and hydrocarbons on nitrous oxide emission was investigated. The membrane bioreactor pilot plant was operated with two phases: i. biomass acclimation by increasing salinity from 10gNaClL(-1) to 20gNaClL(-1) (Phase I); ii. hydrocarbons dosing at 20mgL(-1) with a constant salt concentration of 20gNaClL(-1) (Phase II). The Phase I revealed a relationship between nitrous oxide emissions and salinity. During the end of the Phase I, the activity of nitrifiers started to recover, indicating a partial acclimatization. During the Phase II, the hydrocarbon shock induced a temporary inhibition of the biomass with the suppression of nitrous oxide emissions. The results revealed that the oxic tank was the major source of nitrous oxide emission, likely due to the gas stripping by aeration. The joint effect of salinity and hydrocarbons was found to be crucial for the production of nitrous oxide.

Effect of hydraulic retention time and sludge recirculation on greenhouse gas emission and related microbial communities in two-stage membrane bioreactor treating solid waste leachate

Methane (CH4) and nitrous oxide (N2O) emissions and responsible microorganisms during the treatment of municipal solid waste leachate in two-stage membrane bioreactor (MBR) was investigated. The MBR system, consisting of anaerobic and aerobic stages, were operated at hydraulic retention time (HRT) of 5 and 2.5days in each reactor under the presence and absence of sludge recirculation. Organic and nitrogen removals were more than 80% under all operating conditions during which CH4 emission were found highest under no sludge recirculation condition at HRT of 5days. An increase in hydraulic loading resulted in a reduction in CH4 emission from anaerobic reactor but an increase from the aerobic reactor. N2O emission rates were found relatively constant from anaerobic and aerobic reactors under different operating conditions. Diversity of CH4 and N2O producing microorganisms were found decreasing when hydraulic loading rate to the reactors was increased.