Enhanced denitrification using high-molecular-weight poly(lactic acid) blended with lactide as an effective carbon source

Biodegradable polylactic acid plastic can aid to achieve partial nitrification/denitrification for low carbon to nitrogen ratio wastewater treatment: Performance and microbial mechanism

The partial nitrification/denitrification (PND) process is a green biotechnology for nitrogen removal in low carbon to nitrogen ratio wastewater, however, inhibiting nitrite-oxidizing bacteria (NOB) remains a challenge. This study uncovered that polylactic acid (PLA) can eliminate NOB and regulate the structure and function of nitrogen-transforming bacteria (NTB). An anoxic/aerobic membrane bioreactor with PLA achieved a total nitrogen removal efficiency of 64.8%, much higher than the 32.4% without PLA. Nitrite accumulation during nitrification stage reached 66.7% with PLA addition. Ammonia-oxidizing bacteria were transiently inhibited by PLA but recovered quickly. NOB were maintained at low levels due to the absence of genes for protein and DNA repair, while denitrifiers lacking NarGHI/NapAB genes were enriched. OLB8, with a relative abundance of 13.7%, played a central role in regulating NTB interaction and facilitating PND. In summary, this study provided a new strategy for improving nitrogen removal from wastewater through the reuse of PLA plastics.

Enhanced nitrogen removal from low C/N municipal wastewater in a step-feed integrated fixed-film activated sludge system: Synergizing anammox and partial denitrification with sludge fermentation liquid supplementation

The scarcity of rapidly biodegradable organics, which serve as essential electron donors for the partial denitrification (PD) process, significantly hinders the combined application of PD coupled with anammox (PDA) in municipal wastewater treatment plants. This study innovatively applied, for the first time, a step-feed strategy combined with the use of sludge fermentation liquid (SFL) as an external carbon source in an integrated fixed-film activated sludge (IFAS) system, successfully driving full nitrification and PDA to achieve advanced nitrogen removal from low C/N real municipal wastewater. Moreover, the associated nitrogen removal mechanism of this system was systematically analyzed. By employing second-step SFL feed as a supplementary carbon source, the nitrogen removal efficiency reached 92.26 ± 2.77 % and the effluent total inorganic nitrogen was 6.43 ± 2.23 mg/L, with anammox contributing approximately 70 % to total inorganic nitrogen removal. 16S rRNA gene sequencing and fluorescence in situ hybridization analysis unveiled the extensive cooperation and synergistic interactions among anammox bacteria, denitrifying bacteria, and nitrifying bacteria, with Candidatus Brocadia being highly enriched in biofilms with a relative abundance of 2.21 %. Metagenomic sequencing confirmed that the relative abundance of the narGHI gene was greater than that of the nirS gene, providing stable nitrite accumulation conditions for the anammox process. Overall, this study proposes an innovative synergistic treatment scheme that utilizes a step-feed full nitrification-PDA process driven by SFL to achieve advanced nitrogen removal in municipal wastewater treatment plants. This approach is characterized by low energy consumption, low operational costs and a high nitrogen removal efficiency.

Iron-carbon micro-electrolysis coupled to heterotrophic nitrification aerobic denitrification treating low carbon/nitrogen mariculture wastewater

Considering the unsatisfied nitrogen (N) and phosphorus (P) treatment performance of mariculture wastewater caused by low carbon/nitrogen (C/N), a novel iron-carbon (Fe-C) micro-electrolysis coupled to heterotrophic nitrification aerobic denitrification (HNAD) process was proposed to enhance the N and P elimination. Results revealed that total nitrogen (TN) removal and total phosphorus (TP) removal efficiencies in Fe-C filter with HNAD (R-Fe) increased by 76.1% and 113.3% compared to filter packed with ceramsite (R-C). Fe-C micro-electrolysis reaction led to the decrease of microbial diversity and richness, the enrichment of heterotrophic nitrification aerobic denitrification bacteria (HNADB) and HNAD genes (napA and napB) by 7.3 times and 56.3%. Besides, a synergistic effect existed that Fe-C substances not only further accumulated main functional genes associated with the transformation of N, carbon (C) and iron (Fe), but also indirectly enhanced electron transport system activity and ATP generation, thus resulting in elevating TN removal.

A near-zero-discharge recirculating aquaculture system with 3D-printed poly (lactic acid) honeycomb as solid carbon

A novel near-zero-discharge recirculating aquaculture system was successfully set up and ran for six months or above. A uniquely designed and 3D printed poly (lactic acid) (PLA) structure was applied as carbon source. The system achieved over 50 % daily nitrogen removal capability and maintained a low NO3-N level of <0.5 mg/L. Steady water quality was observed throughout the experiment period. Microbial distribution was studied and top abundant microorganisms and their general functions in carbon and nitrogen utilization were discussed. Denitrification and L-glutamate formation were identified as two main nitrogen pathways. The cooccurrence network connecting various genera and multiple functions was revealed. Subtilisin was one important PLA degrading enzymes in the system.

Bioprocesses for lactic acid production from organic wastes toward industrialization-a critical review

Lactic acid (LA) is a crucial chemical which has been widely used for industrial application. Microbial fermentation is the dominant pathway for LA production and has been regarded as the promising technology. In recent years, many studies on LA production from various organic wastes have been published, which provided alternative ways to reduce the LA production cost, and further recycle organic wastes. However, few researchers focused on industrial application of this technology due to the knowledge gap and some uncertainties. In this review, the recent advances, basic knowledge and limitations of LA fermentation from organic wastes are discussed, the challenges and suitable envisaged solutions for enhancing LA yield and productivity are provided to realize industrial application of this technology, and also some perspectives are given to further valorize the LA fermentation processes from organic wastes. This review can be a useful guidance for industrial LA production from organic wastes on a sustainable view.

Refractory dissolved organic matters in sludge leachate trigger the combination of anammox and denitratation for advanced nitrogen removal

The cost-effective treatment of sludge leachate (SL) with high nitrogen content and refractory dissolved organic matter (rDOM) has drawn increasing attention. This study employed, for the first time, a rDOM triggered denitratation-anammox continuous-flow process to treat landfill SL. Moreover, the mechanisms of exploiting rDOM from SL as an inner carbon source for denitratation were systematically analyzed. The results demonstrated outstanding nitrogen and rDOM removal performance without any external carbon source supplement. In this study, effluent concentrations of 4.27 ± 0.45 mgTIN/L and 5.58 ± 1.64 mgTN/L were achieved, coupled with an impressive COD removal rate of 65.17 % ± 1.71 %. The abundance of bacteria belonging to the Anaerolineaceae genus, which were identified as rDOM degradation bacteria, increased from 18.23 % to 35.62 %. As a result, various types of rDOM were utilized to different extents, with proteins being the most notable, except for lignins. Metagenomic analysis revealed a preference for directing electrons towards NO3--N reductase rather than NO2--N reductase, indicating the coupling of denitratation bacteria and anammox bacteria (Candidatus Brocadia). Overall, this study introduced a novel synergy platform for advanced nitrogen removal in treating SL using its inner carbon source. This approach is characterized by low energy consumption and operational costs, coupled with commendable efficiency.

Boosting the denitrification efficiency of iron-based constructed wetlands in-situ via plant biomass-derived biochar: Intensified iron redox cycle and microbial responses

Considering the unsatisfied denitrification performance of carbon-limited wastewater in iron-based constructed wetlands (ICWs) caused by low electron transfer efficiency of iron substrates, utilization of plant-based conductive materials in-situ for improving the long-term reactivity of iron substrates was proposed to boost the Fe (III)/Fe (II) redox cycle thus enhance the nitrogen elimination. Here, we investigated the effects of withered Iris Pseudacorus biomass and its derived biochar on nitrogen removal for 165 days in ICWs. Results revealed that accumulate TN removal capacity in biochar-added ICW (BC-ICW) increased by 14.7 % compared to biomass-added ICW (BM-ICW), which was mainly attributed to the synergistic strengthening of iron scraps and biochar. The denitrification efficiency of BM-ICW improved by 11.6 % compared to ICWs, while its removal capacity declined with biomass consumption. Autotrophic and heterotrophic denitrifiers were enriched in BM-ICW and BC-ICW, especially biochar increased the abundance of electroactive species (Geobacter and Shewanella, etc.). An active iron cycle exhibited in BC-ICW, which can be confirmed by the presence of more liable iron minerals on iron scraps surface, the lowest Fe (III)/Fe (II) ratio (0.51), and the improved proportions of iron cycling genes (feoABC, korB, fhuF, TC.FEV.OM, etc.). The nitrate removal efficiency was positively correlated with the nitrogen, iron metabolism functional genes and the electron transfer capacity (ETC) of carbon materials (P < 0.05), indicating that redox-active carbon materials addition improved the iron scraps bioavailability by promoting electron transfer, thus enhancing the autotrophic nitrogen removal. Our findings provided a green perspective to better understand the redox properties of plant-based carbon materials in ICWs for deep bioremediation in-situ.

Enhanced chromium and nitrogen removal by constructing a biofilm reaction system based on denitrifying bacteria preferential colonization theory

Understanding the developmental characteristics of microbial communities in biofilms is crucial for designing targeted functional microbial enhancements for the remediation of complex contamination scenarios. The strong prioritization effect of microorganisms confers the ability to colonize strains that arrive first dominantly. In this study, the auto-aggregating denitrifying bacterial Pseudomonas stutzeri strain YC-34, which has both nitrogen and chromium removal characteristics, was used as a biological material to form a stable biofilm system based on the principle of dominant colonization and biofortification. The effect of the biofilm system on nitrogen and chromium removal was characterized by measuring the changes in the quality of influent and effluent water. The pattern of biofilm changes was analyzed by measuring biofilm content and thickness and characterizing extracellular polymer substances (EPS). Further analysis of the biofilm microbiota characteristics and potential functions revealed the mechanism of strain YC-34 biofortified biofilm. The results revealed that the biofilm system formed could achieve 90.56% nitrate-nitrogen removal with an average initial nitrate-nitrogen concentration of 51.9 mg/L and 40% chromium removal with an average initial hexavalent chromium Cr(VI) concentration of 7.12 mg/L. The biofilm properties of the system were comparatively analyzed during the biofilm formation period, the fluctuation period of Cr(VI)-stressed water quality, and the stabilization period of Cr(VI)-stressed water quality. The biofilm system may be able to increase the structure of hydrogen bonds, the type of protein secondary structure, and the abundance of amino acid-like components in the EPS, which may confer biofilm tolerance to Cr(VI) stress and allow the system to maintain a stable biofilm structure. Furthermore, microbial characterization indicated an increase in microbial diversity in the face of chromium stress, with an increase in the abundance of nitrogen removal-associated functional microbiota and an increasing trend in the abundance of nitrogen transfer pathways. These results demonstrate that the biofilm system is stable in nitrogen and chromium removal. This bioaugmentation method may provide a new way for the remediation of heavy metal-polluted water bodies and also provides theoretical and application parameters for the popularization and application of biofilm systems.