Denitrification of aging biogas slurry from livestock farm by photosynthetic bacteria

Effects of zero-valent iron (ZVI) on nitrogen conversion, transformation of sulfamethoxazole (SMX) and abundance of antibiotic resistance genes (ARGs) in aerobic granular sludge process

Even after pre-treatment, livestock and poultry wastewater still contain high concentrations of ammonia and residual antibiotics. These could be removed economically using the aerobic granular sludge (AGS) process with zero-valent iron (ZVI). The interaction of antibiotics and nitrogen in this process needs to be clarified and controlled, however, to achieve good removal performance. Otherwise, antibiotics might generate transformation products (TPs) with higher toxicity and lead to the emergence of antibiotic-resistant bacteria carrying antibiotic resistance genes (ARGs), which could cause persistent toxicity and the risk of disease transmission to the ecological environment. This study investigated the impact of ZVI on AGS for nitrogen and sulfamethoxazole (SMX) removal. The results show that AGS could maintain good ammonia removal performance and that the existence of SMX had a negative impact on ammonia oxidation activities. ZVI contributed to an increase in the abundance of nitrite oxidation bacteria, denitrifying bacteria and the functional genes of nitrogen removal. This led to better total nitrogen removal and a decrease in N2O emission. Accompanied by biological nitrogen transformation, SMX could be transformed into 14 TPs through five pathways. ZVI has the potential to enhance transformation pathways with TPs of lower ecotoxicity, thereby reducing the acute and chronic toxicity of the effluent. Unfortunately, ZVI might enhance the abundance of sul1, sul2, and sul3 in AGS, which increases the risk of sulfonamide antibiotic resistance. In AGS, Opitutaceae, Xanthomonas, Spartobacteria and Mesorhizobium were potential hosts for ARGs. This study provides theoretical references for the interaction of typical antibiotics and nitrogen in the biological treatment process of wastewater and bioremediation of natural water bodies.

Ammonia nitrogen recovery from biogas slurry by SCP production using Candida utilis

The safe and robust yeast Candida utilis was employed for nitrogen recovery as single cell protein from biogas slurry. The maximum biomass of 6.2 g/L with protein content of 53.5% was produced in batch cultivation with glucose as the carbon source, C/N ratio of 3:1, NH₄⁺-N concentration of 3000 mg/L, initial pH of 8.0, and the addition of 0.35% (w/v) Na₂HPO₄. It was speculated that C. utilis can grow well with free ammonia below 197 mg/L. In fed-batch fermentation, a biomass of 14.8 g/L was obtained, and the maintenance of aerobic conditions was critical to improving the production of single cell protein. The sterilized and non-sterilized biogas slurry can be used as an effective pH regulator. The obtained single cell protein was a nutritious, safe, and reliable protein source. This study provides novel insights into nitrogen recovery via C. utilis as a single cell protein from biogas slurry.

Performance of Paracoccus pantotrophus MA3 in heterotrophic nitrification-anaerobic denitrification using formic acid as a carbon source

Excess amount of nitrogen in wastewater has caused serious concerns, such as water eutrophication. Paracoccus pantotrophus MA3, a novel isolated strain of heterotrophic nitrification-anaerobic denitrification bacteria, was evaluated for nitrogen removal using formic acid as the sole carbon source. The results showed that the maximum ammonium removal efficiency was observed under the optimum conditions of 26.25 carbon to nitrogen ratio, 3.39% (v/v) inoculation amount, 34.64 °C temperature, and at 180 rpm shaking speed, respectively. In addition, quantitative real-time PCR technique analysis assured that the gene expression level of formate dehydrogenase, formate tetrahydrofolate ligase, 5,10-methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, respiratory nitrate reductase beta subunit, L-glutamine synthetase, glutamate dehydrogenase, and glutamate synthase were up-regulated compared to the control group, and combined with nitrogen mass balance analysis to conclude that most of the ammonium was removed by assimilation. A small amount of nitrate and nearly no nitrite were accumulated during heterotrophic nitrification. MA3 exhibited significant denitrification potential under anaerobic conditions with a maximum nitrate removal rate of 4.39 mg/L/h, and the only gas produced was N₂. Additionally, 11.50 ± 0.06 mg/L/h of NH₄⁺-N removal rate from biogas slurry was achieved.

Protein recovery as a resource from waste specifically via membrane technology-from waste to wonder

Economic growth and the rapid increase in the world population has led to a greater need for natural resources, which in turn, has put pressure on said resources along with the environment. Water, food, and energy, among other resources, pose a huge challenge. Numerous essential resources, including organic substances and valuable nutrients, can be found in wastewater, and these could be recovered with efficient technologies. Protein recovery from waste streams can provide an alternative resource that could be utilized as animal feed. Membrane separation, adsorption, and microbe-assisted protein recovery have been proposed as technologies that could be used for the aforementioned protein recovery. This present study focuses on the applicability of different technologies for protein recovery from different wastewaters. Membrane technology has been proven to be efficient for the effective concentration of proteins from waste sources. The main emphasis of the present short communication is to explore the possible strategies that could be utilized to recover or restore proteins from different wastewater sources. The presented study emphasizes the applicability of the recovery of proteins from various waste sources using membranes and the combination of the membrane process. Future research should focus on novel technologies that can help in the efficient extraction of these high-value compounds from wastes. Lastly, this short communication will evaluate the possibility of integrating membrane technology. This study will discuss the important proteins present in different industrial waste streams, such as those of potatoes, poultry, dairy, seafood and alfalfa, and the possible state of the art technologies for the recovery of these valuable proteins from the wastewater.

The indispensable role of assimilation in methane driven nitrate removal

Methane is a greenhouse gas that can be released from sludge anaerobic fermentation in wastewater treatment plants. Methane is also an alternative additional carbon source for deep nitrate removal of secondary effluent. A sequencing experiment was conducted to study the efficacy of nitrate removal with methane as the sole carbon source. The maximum nitrate removal rate was 17.2 mg-N·L^-1·d^-1. Nitrate removal was confirmed to arise via two pathways: aerobic methane oxidation coupled to denitrification (AME-D) contributed to 55% of the nitrate removal with the rest stemming from assimilation by methanotrophs. Additional study revealed that nitrate assimilated by methanotrophs was used for the synthesis of proteins, resulting in a protein content of 52.2% dry weight. Metagenomic sequencing revealed a high abundance of nitrate assimilation and glutamine synthetase genes, which were primarily provided by methanotrophs (mainly Methylomonas). Assimilatory nitrate removal by methanotrophs has a high potential for advanced nitrogen removal and for alleviating methane emissions. The nitrogen-rich biomass produced by nitrate absorption could also be used as a biofertilizer for nitrogen recycling.

Nitrogen metabolism in photosynthetic bacteria wastewater treatment: A novel nitrogen transformation pathway

Nitrogen removal from wastewater is a worldwide environmental problem. Photosynthetic bacteria (PSB) were reported to have a great potential in treating varieties of nitrogen-contaminated wastewater. However, their nitrogen metabolic mechanism is still unclear, which was further explored in this work. The results showed that PSB can efficiently utilize NH₄⁺-N, NO₃^--N and NO₂^--N. Over 90% nitrogen removal efficiencies were obtained under suitable condition. 35 ~ 51% of removed nitrogen was transformed to N₂ and N₂O. In addition, basically no mutual transformation occurred between NH₄⁺-N, NO₃^--N and NO₂^--N in PSB, which is different from other biological technologies. Combining with the analysis of functional gene groups, it indicated that there might be a new direct nitrogen transformation pathway, i.e. NH₄⁺ might be directly oxidized to N₂/N₂O in nitrogen metabolism of PSB, which breaks the limitations of existing technologies, and proposed a new understanding of nitrogen metabolism in PSB.

Enhancement of anaerobic digestion effluent treatment by microalgae immobilization: Characterized by fluorescence excitation-emission matrix coupled with parallel factor analysis in the photobioreactor

The bacterial-microalgal consortium has been investigated to anaerobic digestion effluent (ADE) treatment in the photobioreactor (PBR). However, the high concentrations of nutrients reduced the ADE treatment efficiency and the transformation of organic pollutants in PBR was still unclear. In this study, two-sequencing batch PBRs were operated with suspended Microcystis aeruginosa (M. aeruginosa, SMA) and immobilized M. aeruginosa (IMA) to compare the ADE treatment performance. Fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) was conducted to identify organics degradations. The results showed that the proportion of living M. aeruginosa cell (86.4%) in PBR (IMA) was highly significant (p < 0.05) higher than that in PBR (SMA) (75.2%). This indicated immobilized microalgae beads enhanced the resistance to the high concentration of nutrients in PBR (IMA). EEM-PARAFAC analysis displayed the biodegradation order in the bacterial-microalgal consortium system was humic-like substances > tyrosine-like substances > tryptophan-like substances. The removals of humic-like matters (94.05 ± 0.92%) and tyrosine-like matters (91.13 ± 2.49%) in PBR (IMA) were significantly (p < 0.01) higher than those in PBR (SMA). Notably, the average removals of nutrients in PBR (IMA) were significantly (p < 0.05) higher than those in PBR (SMA). This result verified that microalgae immobilization benefitted nutrients removals with 93.05 ± 1.45% of NH₄⁺-N and complete PO₄^3--P removal in PBR (IMA). Moreover, the enrichment of functional genera Flavobacterium and Opitutus contributed to decreasing the organics loadings and strengthening the ADE treatment performance. Therefore, this study verified microalgae immobilization enhanced the actual ADE treatment. Additionally, fluorescent organic pollutants degradations were further evaluated by EEM-PARAFAC analysis in the bacterial-microalgal consortium.

Microbial aerobic denitrification dominates nitrogen losses from reservoir ecosystem in the spring of Zhoucun reservoir

The mechanism and factors influencing nitrogen loss in the Zhoucun reservoir were explored during the spring. The results showed that the nitrate and total nitrogen concentration decreased from 1.84 ± 0.01 mg/L and 2.34 ± 0.06 mg/L to 0.06 ± 0.01 mg/L and 0.48 ± 0.09 mg/L, respectively. Meanwhile, the nitrate and total nitrogen removal rate reached 97.02% ± 0.25 and 79.38% ± 3.32, respectively. Moreover, the abundance of nirS gene and aerobic denitrification bacteria increased from 1.04-3.38 × 10³ copies/mL and 0.71 ± 0.22 × 10² cfu/mL to 5.36-5.81 × 10³ copies/mL and 8.64 ± 2.08 × 10³ cfu/mL, respectively. The low MW fractions of DOM (<5 kDa) increased from 0.94 ± 0.02 mg/L in February to 1.51 ± 0.09 mg/L in April. E3/E4 and absorption spectral slope ratio (S_R) showed that fulvic acid accounted for the main proportion with autochthonous characteristics. These findings were consistent with the fluorescence components and fluorescence characteristic indices based on EEM-PARAFAC. Meanwhile, the microbial metabolism activity increased significantly from February to April, which contributed to the cycle of nutrients within the reservoir water system. Moreover, the abundance of the bacterial species involved in denitrification (Exiguobacterium, Brevundimonas, Deinococcus, Paracoccus, and Pseudomonas) increased significantly. The relative abundance of KOs related to nitrogen metabolism, were initially increased and then decreased. Specifically, K02567 (napA) represented the main proportion of KOs related to denitrification. The abundance of napA-type denitrifying bacteria (Dechloromonas, Pseudomonas, Azospira, Rhodopseudomonas, Aeromonas, Zobellella, Sulfuritalea, Bradyrhizobium, Achromobacter, Enterobacter, Thauera, and Magnetospirillum) increased significantly during the period of nitrogen loss. Furthermore, the levels of nitrate, T, DO, and AWCD were the most important factors affecting the N-functional bacteria composition. The systematic investigation of the nitrogen loss would provide a theoretical foundation for the remediation of the water reservoir via aerobic denitrification in the future.

Enhancement of COD, ammonia, phosphate and sulfide simultaneous removal by the anaerobic photosynthetic bacterium of Ectothiorhodospira magna in batch and sequencing batch culture

An anaerobic photosynthetic bacterium, with chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), total phosphorus (TP) and sulfide (S^2-) simultaneous removal ability, strain SU6, was isolated and identified as belonging to Ectothiorhodospira magna. Its removal efficiencies were simultaneously evaluated in batch culture and influenced in sequencing batch culture. The maximum COD, NH₃-N, TP and S^2- removal rates of 93.04%, 86.70%, 37.55% and 99.99% were obtained in batch culture with an initial pH 8.0 at 35 °C after 72 h. The simultaneous removal efficiency was enhanced in sequencing batch culture, and 789.27 mg/L COD, 68.91 mg/L NH₃-N, 70.20 mg/L S^2- and 5.26 mg/L TP were removed by the end of the last cycle within 24 h. This was the first time of reporting contaminants' simultaneous removal by a pure-cultured photosynthetic bacterium. The experimental results demonstrate that E. magna can efficiently serve as a good candidate in anaerobic wastewater contaminants' simultaneous removal, and maybe as another model anaerobic photosynthetic microorganism for water purification investigations.

Immobilized microalgae for anaerobic digestion effluent treatment in a photobioreactor-ultrafiltration system: Algal harvest and membrane fouling control

A photobioreactor (PBR) coupled with ultrafiltration (UF) system was developed with goals of microalgae cultivation, harvest, and membrane fouling control in the anaerobic digestion effluent purification. Firstly, three-sequencing batch PBRs were started-up with suspended Chlorella vulgaris (C. vulgaris, SCV), immobilized C. vulgaris (ICV) and immobilized C. vulgaris with powdered activated carbon (ICV + PAC). The results exhibited high DOC degradation (66.61%-84.35%) and completely nutrients (nitrogen and phosphorus) removals were attained in PBRs. This indicated bacterial-microalgal consortiums enhanced biodegradation and PAC adsorption accelerated photodegradation. During the microalgae harvest by UF, immobilized microalgae beads protected cells integrity with less debris and intracellular/extracellular organic matters lysis. Moreover, the cake layer in ICV + PAC could even serve as a dynamic layer to entrap the residual pollutants and control membrane fouling. Hence, membrane fouling mitigation and ADE purification were realized during the microalgae harvest process in the ICV + PAC.

Antibiotic resistance genes and intI1 prevalence in a swine wastewater treatment plant and correlation with metal resistance, bacterial community and wastewater parameters

The livestock wastewater treatment plant represents an important reservoir of antibiotic resistance determinants in the environment. The study explored the prevalence of five antibiotic resistance genes (ARGs, including sulI, tetA, qnrD, mphB and mcr-1) and class 1 integron (intI1) in a typical livestock wastewater treatment plant, and analyzed their integrated association with two metal resistance genes (copA and czcA), two pathogens genes (Staphylococcus and Campylobacter), bacterial community and wastewater properties. Results indicated that all investigated genes were detected in the plant. The treatment plant could not completely remove ARGs abundances, with up to 2.2 × 10⁴~3.7 × 10⁸ copies/L of them remaining in the effluent. Mcr-1 was further enriched by 27-fold in the subsequent pond. The correlation analysis showed that mphB significantly correlateed with tetA and intI. Mcr-1 strongly correlated with copA. MphB and intI significantly correlated with czcA. The correlations implied a potential co-selection risk of bacterial resistant to antibiotics and metals. Redundancy analyses indicated that qnrD and mcr-1 strongly correlated with 13 and 14 bacterial genera, respectively. Most ARGs positively correlated to wastewater nutrients, indicating that an efficient reduction of wastewater nutrients would contribute to the antibiotic resistance control. The study will provide useful implications on fates and reductions of ARGs in livestock facilities and receiving environments.

One-step treatment and resource recovery of high-concentration non-toxic organic wastewater by photosynthetic bacteria

In order to achieve simple pollutant removal and simultaneous resource recovery in high-COD-non-toxic wastewater treatment, a one-step photosynthetic bacteria (PSB) method was established using batch study experiment. The effluent COD met the national discharge standard, and biomass with rich protein and high-value substances was efficiently produced. It eliminated the demand of post-treatment for conventional PSB treatment. Results showed that Rhodopseudomonas effectively treated brewery wastewater and achieved biomass proliferation. Yeast extract was the best additive for PSB growth and the effluent COD was below 80 mg/L with 400 mg/L yeast extract, meeting the national discharge standard. In addition, the PSB biomass increased by 2.6 times, and the cells were rich in protein, polysaccharide, carotenoids, bacteriochlorophyll and coenzyme Q10, reaching 420.9, 177.6, 2.53, 10.75 and 38.6 mg/g respectively. This work demonstrated the great potential of PSB for high-COD non-toxic wastewater treatment in one-step process.

Enhancing protein to extremely high content in photosynthetic bacteria during biogas slurry treatment

This work proposed a novel approach to achieve an extremely high protein content in photosynthetic bacteria (PSB) using biogas slurry as a culturing medium. The results showed the protein content of PSB could be enhanced strongly to 90% in the biogas slurry, which was much higher than reported microbial protein contents. The slurry was partially purified at the same time. Dark-aerobic was more beneficial than light-anaerobic condition for protein accumulation. High salinity and high ammonia of the biogas slurry were the main causes for protein enhancement. In addition, the biogas slurry provided a good buffer system for PSB to grow. The biosynthesis mechanism of protein in PSB was explored according to theoretical analysis. During biogas slurry treatment, the activities of glutamate synthase and glutamine synthetase were increased by 26.55%, 46.95% respectively.