Advanced nitrogen removal via nitrite from municipal landfill leachate using a two-stage UASB–A/O system

Nitrogen removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions by simultaneous partial nitrification anammox and denitrification

In this study, a SNAD-SBBR process was implemented to achieve ammonia removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions (0.051 mg/L) for a continuous operation of 266 days. The process demonstrated excellent removal performance, with ammonia nitrogen removal efficiency reaching 100 %, total nitrogen removal efficiency reaching 87.56 %, and an average removal rate of 0.180 kg/(m3·d). The recalcitrant organic compound removal efficiency reached 34.96 %. Nitrogen mass balance analysis revealed that the Anammox process contributed to approximately 98.1 % of the nitrogen removal. Candidatus Kuenenia achieved a relative abundance of 1.49 % in the inner layer of the carrier. In the SNAD-SBBR system, the extremely low DO environment created by the highly efficient partial nitrification stage enabled the coexistence of AnAOB, denitrifying bacteria, and Nitrosomonas, synergistically achieving ammonia removal and carbon reduction. Overall, the SNAD-SBBR process exhibits low-cost and high-efficiency characteristics, holding tremendous potential for landfill leachate treatment.

Continuous flow sequencing bed biofilm reactor bio-digested landfill leachate treatment using electrocoagulation-persulfate

Landfill leachate contains many complex components that have a negative impact on the environment when improperly discharged. This study is the first to treat landfill leachate (after continuous flow sequencing bed biofilm reactor (CF-SBBR) bio-digested) using electrocoagulation (EC) combined with persulfate (PS) on Al and Fe electrodes. The effect of some of the key parameters on the COD, Color, TOC and TN removal efficiencies as part of the EC-PS process were studied using the PS concentration, reaction time, initial pH, current density, and aeration rate. The results show that a PS concentration of 3 g/L improved the COD removal efficiency by 9.0 ± 1.3 % at the Al electrode and 16.0 ± 2.6 % at the Fe electrode. Aeration also improved the COD, TOC and color removal efficiencies by about 10.0 ± 2.3 %, 8.0 ± 1.7 % and 3.0 ± 0.5 % at an optimal aeration rate 3.3 L/min. The optimal operation conditions for the EC-PS process were a PS concentration of 3 g/L, a pH of 2.0 (Al electrode), a pH of 4.0 (Fe electrode), a reaction time of 70 min, a current density of 35 mA/cm² and an aeration rate of 3.3 L/min. The highest COD, color, TOC and TN removal efficiencies were 46.5 ± 1.8 %, 95.8 ± 2.4 %, 83.5 ± 1.7 %, and 40.9 ± 1.6 % at Al electrode and 54.4 ± 2.3 %, 98.5 ± 2.1 %, 78.6 ± 1.5 % and 57.9 ± 1.1 % at the Fe electrode. The EC-PS working mechanisms involve co-precipitation, an advanced oxidation process (AOPs) using oxidation radicals (HO, SO₄^-) and flotation. EC-PS is a promising method to treat bio-digested landfill leachate.

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.

Rapid start-up and stable maintenance of partial nitrification-anaerobic ammonium oxidation treatment of landfill leachate at low temperatures

The current research regarding anaerobic ammonium oxidation (anammox) for the treatment of landfill leachate mainly focuses on a temperature range of 30-35 °C. However, achieving and maintaining anammox at lower temperatures would widen its application for the treatment of landfill leachate. This study, attempts to address this issue by using a combined process involving an upflow anaerobic sludge blanket (UASB), anoxic/oxic (A/O) reactor, anammox reactor (ANAOR), and anaerobic sequencing batch reactor (ASBR) to enrich anammox bacteria at relatively low temperatures. The rapid start-up of the partial nitrification-anammox process for landfill leachate treatment was achieved and maintained at 13-22 °C. The experiment was divided into phase 1 (20-22 °C) and phase 2 (13-15 °C). The results showed that 87.1% of the chemical oxygen demand (COD), 97.4-97.7% of the ammonium nitrogen (NH₄⁺-N), and 93.3-94.7% of the total nitrogen (TN), were removed. At least 29.3% and 11.4% of NH₄⁺-N was removed through anammox in phases 1 and 2, respectively, with an accumulation NO₂^--N ratio of 86.1-88.6%. Candidatus Kuenenia was the dominant anammox bacteria in the anammox process. A low temperature of 13-15 °C did not affect ammonia oxidizing bacteria (AOB), and their relative abundance in the A/O reactor ranged from 27.29% to 33.22%.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Cooperation between partial-nitrification, complete ammonia oxidation (comammox), and anaerobic ammonia oxidation (anammox) in sludge digestion liquid for nitrogen removal

The challenge of sludge digester liquor treatment is its high ammonium nitrogen (NH₄⁺-N) concentration. Early reports found that complete ammonia oxidation (comammox) was not present and anaerobic ammonia oxidation (anammox) was difficult to achieve in most sludge digester liquor treatments. In this study, NH₄⁺-N removal by cooperation between partial-nitrification, comammox, and anammox processes was achieved in a sequencing batch reactor (SBR) for sludge digester liquor treatment. The results showed that 2100-2200 mg/L of NH₄⁺-N was removed in the SBR with 98.82% removal efficiency. In addition, 55.11% of NH₄⁺-N was converted to nitrite nitrogen (NO₂^--N) by partial-nitrification, 25.43% of NH₄⁺-N was converted to nitrate nitrogen (NO₃^--N) by comammox, and 18.28% of NH₄⁺-N was removed by anammox. During the operation, in the SBR, the relative abundance of the dominant ammonia-oxidizing bacteria (Chitinophagaceae) was 18.89%, that of the dominant anammox bacteria (Candidatus Kuenenia) was 0.10%, and that of the dominant comammox bacteria (Nitrospira) was 0.20%. Therefore, the high nitrogen removal efficiency in this system was considered the result of the combination of the three processes. These results showed that comammox and anammox could play very important roles in nitrogen transformation and energy-saving in nitrogen removal systems.

Low energy treatment of landfill leachate using simultaneous partial nitrification and partial denitrification with anaerobic ammonia oxidation

An up-flow anaerobic sludge blanket reactor (UASB), anoxic/oxic (A/O)-anaerobic ammonia oxidation reactor (ANAOR or anammox reactor), and anaerobic sequencing batch reactor (ASBR) were employed in the treatment of landfill leachate with partial nitrification-anammox and half-denitrification-anammox. The Chemical Oxygen Demand (COD) concentration, ammonium nitrogen (NH₄⁺-N) concentration, and total nitrogen (TN) concentration of the basal leachate was 2200-2500 mg/L, 1200-1300 mg/L, and 1300-1400 mg/L, respectively. After a 1:2 dilution using domestic sewage, the COD, NH₄⁺-N, and TN concentrations in the influent were 800-1000 mg/L, 400-430 mg/L, and 420-440 mg/L, respectively. After treatment, the final COD, NH₄⁺-N, and TN were decreased to 90-100 mg/L, 13-14 mg/L, and 35-38 mg/L, respectively. In the ASBR, organic carbon sources in sewage-diluted landfill leachate were introduced for the conversion of nitrate nitrogen (NO₃^--N) into nitrite nitrogen (NO₂^--N). This enabled the continued reaction of NO₂^--N with NH₄⁺-N from the newly introduced sewage-diluted landfill leachate via anammox. As a result, complete TN removal was achieved in the system. Microbial diversity analysis indicated that the relative abundance of ammonia-oxidizing bacteria (AOB) was four to five times greater than nitrite-oxidizing bacteria (NOB) in the A/O reactor, showing that partial nitrification was prevalent. The relative abundance of the anammox bacterium Candidatus Kuenenia gradually increased in each reactor, reaching a maximum of 1.17%-1.39%. Using this set-up, we achieved advanced, efficient, and economical, COD reduction and nitrogen removal. Taken together, the findings provide important insights into the optimal operation of landfill leachate treatments.

Continuous-flow combined process of nitritation and ANAMMOX for treatment of landfill leachate

Due to the difficulty in removing nitrogen from landfill leachate, a combined continuous-flow process of nitritation and anammox was applied to process mature leachate. The transformation rate of ammonia and nitrite accumulation ratio in A/O reactor were kept above 95% and 92% respectively through associated inhibition of free ammonia (FA) and free nitrous acid (FNA) to NOB. The total nitrogen volumetric load of anammox in an UASB reactor was brought up from 0.5kg/(m(3)·d) to 1.2kg/(m(3)·d) by gradually increasing influent substrate concentration and reducing hydraulic retention time (HRT). The results show that COD from mature leachate did not bring obvious inhibition effects to anammox. Under concentrations of influent ammonia and COD which were respectively 1330mg/L and 2250mg/L, the removal efficiencies of TN and COD reached 94% and 62% respectively. In the quantitative PCR reactions, the proportions occupied by AOB, NOB and anammox in A/O were 11.39%, 1.76% and 0.05% respectively; and proportions of those in UASB were 0.35%, 4.01% and 7.78% respectively.