Effect of alkalinity on bio-zeolite regeneration in treating cold low-strength ammonium wastewater via adsorption and enhanced regeneration

Solution, exchangeable and fixed ammonium in natural diatomite as a simulated PRB material: effects of adsorption and bioregeneration processes

Ammonia nitrogen (NH₄⁺-N) is widely found in aquifers with strong reducibility or poor adsorptivity as a dissolved inorganic nitrogen pollutant. The application of adsorbents with effective long-term in situ bioregeneration as permeable reactive barrier (PRB) media for nitrogen removal has raised concern. In this study, the advantage of natural diatomite as a PRB material was investigated by exploring its NH₄⁺-N adsorption and desorption characteristics, and the ability of diatomite and zeolite to be loaded nitrifying bacteria was also compared. The results showed that the exchangeable ammonium from chemical-monolayer adsorption was the main form of NH₄⁺-N and was adsorbed by diatomite. Moreover, the adsorption process was limited with a maximum adsorption capacity of 0.677 mg g^-1. However, diatomite demonstrated an excellent loading of aerobic-heterotrophic microorganisms, even stronger than zeolite. Compared with zeolite reactors, a higher OD₆₀₀ value of nitrifiers, a faster NH₄⁺-N degradation rate and more abundant functional genes were observed during the bioregeneration process of diatomite. Both the solution and exchangeable ammonium forms were bioavailable, and the regeneration of diatomite was more than 80.0% after two days. Moreover, desorption-biodegradation was systematically analysed to determine the bioregeneration mechanism of diatomite. Diatomite with good regeneration ability can be used as a competitive alternative to address sudden nitrogen pollution.

Physico-chemical processes

By summarizing 187 relevant research articles published in 2019, the review is focused on the research progress of physicochemical processes for wastewater treatment. This review divides into two sections, physical processes and chemical processes. The physical processes section includes three sub-sections, that is, adsorption, granular filtration, and dissolved air flotation, whereas the chemical processes section has five sub-sections, that is, coagulation/flocculation, advanced oxidation processes, electrochemical, capacitive deionization, and ion exchange. PRACTITIONER POINTS: Totally 187 research articles on wastewater treatment have been reviewed and discussed. The review has two major sections with eight sub-topics.

Biological nitrogen removal via combined processes of denitrification, highly efficient partial nitritation and Anammox from mature landfill leachate

The combined processes of pre-denitrification, highly efficient partial nitritation and Anammox were developed to treat mature landfill leachate. In the partial nitritation stage, an outstanding nitrite production rate (NPR) of approximately 1.506 kg·(m³ day)^-1 of mature landfill leachate was achieved in a zeolite biological aerated filter (ZBAF) due to the inhibition of nitrite-oxidizing bacteria (NOB) by free ammonia (FA) and free nitrous acid (FNA). With respect to the nitrogen removal performance of the combined process, remarkable nitrogen removal efficiencies (NRE) and nitrogen removal rates (NRR), which exceeded 90.0% and 0.490 kg·(m³ day)^-1, respectively, were detected based on the stable and efficient partial nitritation performance and reasonable control of effluent nitrite to ammonium ratios (at approximately 1.2) in the ZBAF. High-throughput sequencing analysis further revealed that the dominant bacteria genera Paracoccus and Comamonas in the denitrification reactor, Nitrosomonas in the ZBAF and Candidatus Kuenenia and Candidatus Anammoxoglobus in the Anammox reactor were demonstrated to be responsible for denitrification, partial nitritation and Anammox process, respectively.

Nitrite accumulation stability evaluation for low-strength ammonium wastewater by adsorption and biological desorption of zeolite under different operational temperature

How to achieve stable nitrite accumulation was still a huge challenge for low-carbon and energy-saving biological nitrogen removal of low-strength ammonium wastewater. This study proposed a new way to solve this problem with zeolite biological fixed bed (ZBFB) by cycle operation of adsorption and biological desorption. In order to evaluate nitritation performance of this reactor, the influence of operational temperature on nitrite accumulation stability was investigated by 126 cycles operation in four parallel ZBFB reactors for low-strength ammonium wastewater (50 mg/L NH₄⁺-N). It was found that higher operational temperature (i.e., 36.0 °C), rather than other temperature (i.e., 27.0 °C, 30.0 °C, 33.0 °C), could maintain stable nitrite accumulation with nitrite production rate of 0.312 kg NO₂^--N·m^-3 zeolite·day^-1 and nitrite accumulation ratio higher than 95.0% after biological desorption. High-throughput sequencing analysis results showed that bacterial structure significantly changed in ZBFB under different operational temperature, and obvious enrichment of genus Nitrosomonas (AOB) and gradually enhanced free ammonia (FA) inhibition on genus Nitrospira and Nitrobacter (NOB) were found by elevation of operational temperature, leading to different nitrite accumulation performance in ZBFB reactors. The mechanism for stable nitrite accumulation performance by ZBFB might be attributed to overwhelming growth rate of AOB than NOB, faster ammonium desorption and enhanced FA inhibition on NOB under operational temperature (i.e., 36.0 °C). All in all, keeping high temperature for biological desorption step should be extremely crucial for stable nitrite accumulation by ZBFB, which could facilitate further low-carbon and energy-saving biological nitrogen removal for low-strength ammonium wastewater treatment.