Nitrification mainly driven by ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in an anammox-inoculated wastewater treatment system

Study of bacterial population dynamics in seed culture developed for ammonia reduction from synthetic wastewater

The waterbodies have been polluted by various natural and anthropogenic activities. The aquatic waste includes ammonia as one of the most toxic pollutants. Several biological treatment systems involving anoxic and semi anoxic bacteria have been proposed for reducing nitrogen loads from wastewater and increasing the efficiency and cost effectiveness. These bacteria play a vital role in the processes involved in the nitrogen cycle in nature. However, the enrichment, sustainability and identification of bacterial communities for wastewater treatment is an important aspect. Most of the chemolithotrophs are unculturable hence their identification and measurement of abundance remains a challenging task. In this study the different bacteria involved in total nitrogen removal from the wastewater are enriched for 700 days under anoxic condition. The synthetic wastewater containing 0.382 g/L of ammonium chloride was used. Molecular identification of the bacteria involved in various steps of the nitrogen cycle was carried out based on amplification of functional genes and 16S rRNA gene Polymerase chain reaction followed by DNA sequencing. Change in the abundance of chemolithotrophs was studied using qPCR. The mutual growth of various nitrifiers along with anaerobic bacteria were identified by molecular characterisation of DNA at various time intervals with the different genes involved in the nitrogen cycle. Nitrosomonas species like Nitrosomonas europaea were identified throughout the batch scale studies possessing the genes associated with ammonia oxidizing bacteria and nitrite oxidizing bacteria which act as a complete ammonia oxidizer. The uncultured species of Nitrospira and anammox bacteria were also observed which predicts the coexistence of the anammox and comammox bacteria in a batch scale study. The coexistence of the semi anoxic and anoxic bacteria helped in the growth of these bacteria for a longer duration of time. The nitrite produced by the comammox during nitrification can be utilized by anammox as an electron carrier. The other species of denitrifiers like Pseudomonas denitrificans and Aminobacter aminovorans were also observed. It is concluded that the enrichment of semi anoxic and anoxic bacteria was faster with the increase in growth of the bacteria involved in nitrification, comammox, anammox and partial denitrification process. The bacterial growth is enhanced and the efficiency is increased which can be further used in the development of small pilot scale bioreactor for total nitrogen removal.

Optimizing total ammonia-nitrogen concentration for enhanced microbial fuel cell performance in landfill leachate treatment: a bibliometric analysis and future directions

Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia-nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011-2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject's ten most productive universities. Most studies found that maintaining TAN concentrations in the 400-800 mg L-1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.