Carbon Source For Denitrification Research Articles

Life cycle carbon footprints of alternative sludge pretreatment technologies to recover carbon sources for denitrification

Life cycle carbon footprints of alternative sludge pretreatment technologies to recover carbon sources for denitrification

Disintegrated Waste-Activated Sludge (NO2/FNA Method) as a Source of Carbon for Denitrification in the Mainstream of a WWTP

The deficiency of readily biodegradable organic carbon can be a significant limitation to effective nitrogen removal during wastewater denitrification. Waste-activated sludge (WAS) is a source of carbon produced directly at wastewater treatment plants (WWTPs). Raw WAS has a large molecular weight and complex chemical structure molecules that are not easily available for microorganisms. In this study, easily biodegradable organic fractions were released using pH control and/or nitrites and nitric acid (NO2/FNA). The obtained results indicated that WAS can be a sufficient carbon source for denitrification in WWTPs that are at risk of minor effluent violations. The implementation of WAS disintegration with the use of pH control and NO2/FNA allowed for the denitrification of an additional 0.5 and 0.8 mgN-NO3/L. WAS disintegration, besides being a source of carbon generation, reduces the volume of sludge and leads to the implementation of a closed-loop system.

Microbial interactions facilitating efficient methane driven denitrification via in-situ utilization of short chain fatty acids

High nitrate pollution in agriculture and industry poses a challenge to emerging methane oxidation coupled denitrification. In this study, an efficient nitrate removal efficiency of 100 % was achieved at an influent loading rate of 400 mg-N/L·d, accompanied by the production of short chain fatty acids (SCFAs) with a maximum value of 80.9 mg/L. Batch tests confirmed that methane was initially converted to acetate, which then served as a carbon source for denitrification. Microbial community characterization revealed the dominance of heterotrophic denitrifiers, including Simplicispira (22.8 %), Stappia (4.9 %), and the high‑nitrogen-tolerant heterotrophic denitrifier Diaphorobacter (19.0 %), at the nitrate removal rate of 400 mg-N/L·d. Notably, the low abundance of methanotrophs ranging from 0.24 % to 3.75 % across all operational stages does not fully align with the abundance of pmoA genes, suggesting the presence of other functional microorganisms capable of methane oxidation and SCFAs production. These findings could facilitate highly efficient denitrification driven by methane and contributed to the development of denitrification using methane as an electron donor.

Denitrification Performance and Microbiological Mechanisms Using Polyglycolic Acid as a Carbon Source

When treating municipal wastewater, nitrogen removal is often limited due to low C/N, which needs to be compensated for by additional carbon source injections. This study investigated the feasibility of using industrial-waste polyglycolic acid (PGA) as a carbon source for denitrification in an SBR to obtain an economical carbon source. The results revealed that an optimal denitrification performance in a methanol-fed activated sludge system was achieved with a PGA dosage of 1.2 mL/L, a pH of 7–8, and a dissolved-oxygen (DO) concentration of 3 ± 0.5 mg/L. Under these conditions, all quality parameters for effluent water met the required criteria [COD < 50 mg/L; TN < 15 mg/L; NH4+-N < 5(8) mg/L]. PGA enhanced the variety and richness of microbial communities, thereby markedly increasing the relative abundance of major phyla such as Proteobacteria and Bacteroidota and major genera such as Paracoccus and Dechloromonas. Furthermore, PGA upregulated the expression of nitrogen-metabolism-related genera, including amo, hao, nar, and nor, which improved the denitrification performance of the system. This study provides a reference for applying PGA as a carbon source for low-C/N-wastewater treatment and solid-waste utilization.

The superiority of citrate as denitrification carbon source in an activated sludge system: Substrate metabolism, electron transfer and microbial characteristics

Citrate, a low-molecular-weight organic substance, was rich in citric acid production wastewater with the potential for reuse. Although citrate has been extensively used as a denitrification carbon source, previous studies mainly focus on its application by pure cultures of denitrifying bacteria. The information about denitrification performance and mechanisms using citrates as carbon source in an activated sludge system is still very limited. This study investigated the denitrification efficiency and mechanisms using citrate as carbon source through a long-term operation of continuous reactor. Under the C/N ratio of 5, the total nitrogen (TN) removal efficiency using citrate as carbon source was 93.21 ± 4.24 %, which was comparable to that of acetate (99.84 ± 0.44 %), and much higher than glucose (65.64 ± 3.86 %). Higher denitrification rate was achieved using citrate as carbon source, which was slightly higher than acetate and >4 times of that using glucose. Due to the high activities of denitrifying enzymes including nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (N2OR), there was almost no NO2‐-N and N2O accumulation in the reactor fed with citrate, which was superior to the reactors fed with acetate or glucose. Azoarcus (48.2 %) with the ability of complete denitrification was the most dominant bacteria in the reactor fed with citrate. Considering denitrification kinetics, activities of key enzymes and microbial community characteristics, citrate had a superiority as an effective denitrification carbon source.

Insights into feasibility and microbial characterizations on simultaneous elimination of dissolved methane from anaerobic effluents and nitrate/nitrite reduction in a conventional anoxic reactor with magnetite

Discovery of nitrate/nitrite-dependent anaerobic methane oxidation (DAMO) challenges the conventional biological treatment processes, since it provides a possibility of simultaneously mitigating dissolved methane emissions from anaerobic effluents and reducing additional carbon sources for denitrification. Due to the slow growth of specialized DAMO microbes, this possibility has been just practiced with biofilms in membrane biofilm reactors or granular sludge in membrane bioreactors. In this study, simultaneous elimination of dissolved methane from anaerobic effluents and nitrate/nitrite reduction was achieved in a conventional anoxic reactor with magnetite. Calculations of electron flow balance showed that, with magnetite the eliminated dissolved methane was almost entirely used for nitrate/nitrite reduction, while without magnetite approximately 52 % of eliminated dissolved methane was converted to unknown organics. Metagenomic sequencing showed that, when dissolved methane served as an electron donor, the abundance of genes for reverse methanogenesis and denitrification dramatically increased, indicating that anaerobic oxidation of methane (AOM) coupled to nitrate/nitrite reduction occurred. Magnetite increased the abundance of genes encoding the key enzymes involved in whole reverse methanogenesis and Nir and Nor involved in denitrification, compared to that without magnetite. Analysis of microbial communities showed that, AOM coupled to nitrate/nitrite reduction was proceeded by syntrophic consortia comprised of methane oxidizers, Methanolinea and Methanobacterium, and nitrate/nitrite reducers, Armatimonadetes_gp5 and Thauera. With magnetite syntrophic consortia exchanged electrons more effectively than that without magnetite, further supporting the microbial growth.

Evaluation of aircraft deicing fluid as an external carbon source for denitrification

Water resource recovery facilities (WRRFs) performing biological nitrogen removal (BNR) often require external carbon sources for meeting nitrogen discharge permit limits. This brings an additional financial burden to the facilities considering the continuous need of these external carbon sources. This paper evaluates the utilization of airport stormwater, which in the winter season is rich in aircraft deicing fluid (ADF) as an alternative external carbon source. Denitrification and nitrification bench scale experiments were performed to assess the efficacy of external carbon sources to remove nitrogen in WRRFs. Experimental results showed that ADFs achieve denitrification rates of 0.064–0.066 d−1, higher than what achieved by a commercial carbon source, MicroC 2000A, with corresponding value of 0.058 d−1 at low temperatures, as low as 13 °C, which is considered a worst-case scenario for nitrogen removal efficiency. Furthermore, no inhibition to nitrification associated with the ADFs was observed. Subsequently a dynamic modeling study was conducted to assess the performance of ADFs as external carbon sources for denitrification and compared them to the conventional source that was being used in a full-scale BNR process. Results from the dynamic modeling study revealed that if 40 % of the spent-ADF at LaGuardia airport, New York City, could be collected with the stormwater and conveyed to a WRRF via the sewer collection system, an approximate reduction of 30 % of the commercial external carbon source could be accomplished by repurposing a waste product. This study contributes to the potential of ADF as a denitrification aid and an alternative for commercially available carbon sources with comparable nitrogen removal efficiencies.

Novel insights into the co-metabolism of pyridine with different carbon substrates: Performance, metabolism pathway and microbial community

Pyridine is a widely employed nitrogen-containing heterocyclic organic, and the discharge of pyridine wastewater poses substantial environmental challenges due to its recalcitrance and toxicity. Co-metabolic degradation emerged as a promising solution. In this study, readily degradable glucose and the structurally analogous phenol were used as co-metabolic substrates respectively, and the corresponding mechanisms were thoroughly explored. To treat 400 mg/L pyridine, all reactors achieved remarkably high removal efficiencies, surpassing 98.5%. And the co-metabolism reactors had much better pyridine-N removal performance. Batch experiments revealed that glucose supplementation bolstered nitrogen assimilation, thereby promoting the breakdown of pyridine, and resulting in the highest pyridine removal rate and pyridine-N removal efficiency. The high abundance of Saccharibacteria (15.54%) and the enrichment of GLU and glnA substantiated this finding. On the contrary, phenol delayed pyridine oxidation, potentially due to its higher affinity for phenol hydroxylase. Nevertheless, phenol proved valuable as a carbon source for denitrification, augmenting the elimination of pyridine-N. This was underscored by the abundant Thauera (30.77%) and Parcubacteria (7.21%) and the enriched denitrification enzymes (narH, narG, norB, norC, and nosZ, etc.). This study demonstrated that co-metabolic degradation can bolster the simultaneous conversion of pyridine and pyridine-N, and shed light on the underling mechanism.

Denitrification Capacity of Volatile Fatty Acids from Sludge Fermentation: Lab-Scale Testing and Full-Scale Assessment

This work provides insights into the possibility of integrating recovered volatile fatty acids (VFAs) into biological nitrogen removal processes. VFAs are the main products of the acidogenic fermentation of waste sludge and are an effective carbon source for denitrification in activated sludge processes. The assessment of denitrification rates and the utilisation hierarchy of different VFAs are relevant to evaluating the possibility of replacing external carbon sources with the fermented liquid, FL, from acidogenic fermentation. To this scope, single VFAs, FL collected from a full-scale waste sludge fermenter, and commercial hydroalcoholic solutions have been tested with manometric lab-scale tests. Regarding single acids, acetic acid showed the highest denitrification rates, up to 4 mg N-NO3 g VSS−1 h−1, while more complex acids usually showed a lower denitrification rate. The synthetic VFA mixture and FL showed a higher denitrification rate than the sole acetate (up to 134% of the acetate denitrification rate). Mass balances across the full-scale wastewater treatment plant demonstrated the positive role of FL dosage in enhancing the denitrification process in the activated sludge treatment, with an average nitrogen removal equal to 57% and 78% without and with FL dosage, respectively. Batch manometric tests proved to be an efficient and reliable tool to assess the quality of the carbon sources as well as the activity of denitrifying bacteria in activated sludge samples.

Applying sludge hydrolysate as a carbon source for biological denitrification after composition optimization via red soil filtration

Sludge hydrolysate, the byproduct generated during sludge hydrothermal treatment (HT), is a potential carbon source for biological denitrification. However, the refractory organic matters and the nutrient substances are unfavorable to the nitrogen removal. In this study, effects of HT conditions on the hydrolysate properties, and the hydrolysate compositions optimization via red soil (RS) filtration were investigated. At HT temperature of 160–220 °C and reaction time of 1–4 h, the highest dissolution rate of organics from sludge to hydrolysate achieved 70.1 %, while the acetic acid dominated volatile fatty acids (VFAs) was no more than 5.0 % of the total organic matter content. The NH4+-N and dissolved organic nitrogen (DON) were the main nitrogen species in hydrolysate. When the hydrolysate was filtered by RS, the high molecular weight organic matters, DON, NH4+ and PO43− were effectively retained by RS, while VFAs and polysaccharide favorable for denitrification were kept in the filtrate. When providing same COD as the carbon source, the filtrate group (Fi-Group) introduced lower concentrations of TN and humic substances but higher content of VFAs. This resulted in TN removal rate (57.0 %) and denitrification efficiency (93.6 %) in Fi-Group higher than those in hydrolysate group (Hy-Group), 39.4 % and 83.7 %, respectively. It is noticeable that both Hy- and Fi- Groups up-regulated most of denitrification functional genes, and increased the richness and diversity of denitrifying bacteria. Also, more denitrifying bacteria genera appeared, and their relative abundance increased significantly from 3.31 % in Control to 21.15 % in Hy- Group and 31.31 % in Fi-Group. This indicates that the filtrate is a more suitable carbon source for denitrification than hydrolysate. Moreover, the pH rose from 4.6 ± 0.14 to 6.5 ± 0.05, and the organic carbon, TN, TP and cation exchange capacity (CEC) of RS increased as well after being filtered, implying that the trapped compounds may have the potential to improve soil quality. This study provides a new insight for hydrolysate application according to its composition characteristics, and helps make the most use of wasted sludge.

The dual role of potassium ferrate in promoting primary sludge hydrolysis and acidogenesis in anaerobic fermentation

Potassium ferrate (PF), a green disinfectant has been widely used in drinking water disinfection and has drawn immense attention for its application in sludge treatment. This research study has investigated the effects of PF on the hydrolysis and acidification of primary sludge (PS) to promote the short chain fatty acids (SCFAs) recovery, while achieving solid waste treatment and carbon emission reduction. The results showed that PF could effectively promote the accumulation of SCFAs, and maximum SCFAs yield of 4686.56 mg COD/L was achieved by PF assisted PS fermentation at a PF dosage of 0.4 g/g VSS, which was 2.05 times higher than the control. Substance transformation and enzyme activity analysis indicated that PF significantly promoted the release and hydrolysis of insoluble organic matters from PS through chemical oxidation and alkaline hydrolysis. Furthermore, high doses of PF could also inhibit the growth of methanogens and alter the dominant fermentation flora responsible for SCFAs production. Under the influence of high-dose PF, the foremost acidogenic bacteria were shifted into Trichococcus, Enterococcus, Streptococcus and Gallicola, which might be selectively enriched under the stress of residual Fe (Ⅲ) in the system. The PS fermentation liquid produced after PF pretreatment exhibited a higher C/N ratio and lower phosphorus concentration, which enhanced its suitability as carbon sources for denitrification in WWTPs. This study offered an environmentally friendly method for recovering SCFAs from PS and provided a viable approach to addressing the issue of carbon source shortage in wastewater treatment processes.

Is nitrification inhibition the bottleneck of integrating hydrothermal liquefaction in wastewater treatment plants?

Sewage sludge management poses challenges due to its environmental impact, varying composition, and stringent regulatory requirements. In this scenario, hydrothermal liquefaction (HTL) is a promising technology for producing biofuel and extracting phosphorus from sewage sludge. However, the toxic nature of the resulting process water (HTL-PW) raises concerns about integrating HTL into conventional wastewater treatment processes. This study investigated the inhibitory effects of HTL-PW on the activity of the main microbial functions in conventional activated sludge. Upon recirculation of the HTL-PW from the excess sludge into the wastewater treatment plant, the level of COD in the influent is expected to increase by 157 mgO2⋅L−1, resulting in 44% nitrification inhibition (IC50 of 197 mg⋅L−1). However, sorption of inhibitory compounds on particles can reduce nitrification inhibition to 27% (IC50 of 253 mg⋅L−1). HTL-PW is a viable carbon source for denitrification, showing nearly as high denitrification rates as acetate and only 17% inhibition at 157 mgO2⋅L−1 COD. Under aerobic conditions, heterotrophic organic nitrogen and organic matter conversion remains unaffected up to 223 mgO2⋅L−1 COD, with COD removal higher than 94%. This study is the first to explore the full integration of HTL in wastewater treatment plants for biofuel production from the excess activated sludge. Potential nitrification inhibition is concerning, and further long-term studies are needed to fully investigate the impacts.

Microbiological Mechanisms for Nitrogen Removal Using Anaerobic Fermentation Liquid from Spent Mushroom Substrates as a Carbon Source

In wastewater treatment, a low C/N ratio highly inhibits the bioremoval of nitrogen, and commercial external carbon sources are widely used. In order to obtain an economical substitute, fermentation broth of spent mushroom substrates (SMS) was employed here as a carbon source for denitrification in a sequencing batch reactor (SBR). During the domestication process, the SMS fermentation broth-feeding treatment presented comparable nitrogen removal ability (74.44%) with a commercial carbon source group (77.99%). Rhodobacter, Lactobacillus and Pseudomonas were the dominant bacteria in the fermentation broth, and Saccharomycetales Gymnopilus dilepis was the dominant fungi. At the early domestication stage, the relatively high concentration of fermentation broth led to a much lower abundance of typical nitrate reductase genes than the control group. Furthermore, extracellular polymeric substance (EPS) formation was observed in the broth-feeding sample. The microbial structure dynamic was investigated, which showed a high influent effect when 20% fermentation broth was added. As domestication proceeded, similar dominant species in the control and broth-feeding treatments were observed. Overall, SMS fermentation broth can be used as a promising substitute to replace a costly commercial carbon source.

Material and C/N flow analyses of alternative sludge pretreatment technologies for recovering carbon sources for denitrification

Sewage sludge can serve as a carbon source for denitrification after pretreatment and hydrolysis. However, existing technologies have various technical routes and performances for carbon recovery and nitrogen release. To evaluate the abilities of different technologies to recover carbon sources, material and elemental flow analyses were performed by parameterising and balancing the sludge compositions and conversion coefficients based on 139 datasets. Technological routes with alkali/thermal and alkali/H2O2/microwave treatments statistically achieved the highest yields of volatile soluble solids, and those with thermal and mechanical treatments dissolved the most nitrogen during pretreatment. The technological route with alkali/thermal treatment achieved the highest effective carbon source of 191 g/kg of initial total solid on average when the potential carbon consumption by the yielded soluble total nitrogen and phosphorus was subtracted. This study provides important statistical evidence for the development and comparison of alternative technologies for recovering carbon sources from sludge for denitrification.

Novel slow-release carbon source improves anodic denitrification and electricity generation efficiency in microbial fuel cells

MFC anodic denitrification is more suitable for the coexistence of organic matter and nitrate in actual sewage, but the traditional carbon source has some problems such as high cost and difficulty of dosage control in MFC. Herein, corncob and polycaprolactone (PCL) were mechanically pulverized and mixed in the system of polyvinyl alcohol and sodium alginate, and cross-linked to prepare slow-release carbon source fillers (CPSP), which were added to the MFC anolyte to realize the coupling of solid-phase denitrification and anodic denitrification. Results showed the start-up period of MFC experimental group (MFC-C) with CPSP was slightly longer than the control group (MFC-0), but MFC-C's maximum output voltage (648.4 mV) and power density (2738 mW/m3) could be increased by 5% and 15% higher than that of MFC-0 (P < 0.05). The degradation process of MFC substrate in unit cycle was mainly divided into nitrogen removal stage (0–8 h) and electricity generation stage (8–48 h). The NO3−-N and COD degradation and power generation kinetic processes of MFC conformed to the Han-Levenspiel model. Kinetics experiments showed CPSP can improve the affinity and tolerance of MFC to NO3−-N, also it can alleviate the pressure of electron competition in anolyte and improve coulombic efficiency. In addition, microbial communities were significantly changed under the effect of CPSP (P < 0.001). Meanwhile, CPSP can promote the synthesis of denitrification functional genes. This study provides a new strategy to improve the performance of MFC by the addition of novel denitrification carbon source.

Granular biomass technology for providing drinking water: microbial versatility and nitrate performance in response to carbon source

The aerobic granular biomass technology was optimized for treating nitrate-polluted groundwater based on the biological denitrification processes in order to provide drinking water. Reactors inoculated with granular biomass were operated at progressively lower C/N rate using acetate and methanol to encourage heterotrophic denitrification, in order to meet the recommended requirements described by European Drinking Water Framework Directive. The granulation and long-term stability of granular biomass under low C/N were successful for all stages, demonstrated compactness of granules and absence of filamentous microorganisms. The nitrate removal was similar in methanol- and acetate-fed reactors, occurring in both cases nitrate removal ratios > 80%, and fact allows the selection of one of both depending groundwater polluted case. Also, feeding reactors with 2 C/N ratio showed nitrate removal values of ≥ 95%, treating highly polluted groundwater (100 mg·L−1). The microbial diversity was higher in the methanol-fed reactor with representative phylotypes as Flavobacterium, Cytophagaceae, NS9 marine group, while species richness was higher in the acetate-fed reactor, which was mainly represented by Flavobacterium genus. Statistical analyses revealed the higher resilience of bacterial population on granules fed with acetate, showing more resistance under drop C/N ratio. Oscillating pollution in groundwater during seasonal periods should be treated using acetate as carbon source for denitrification carried out by granular biomass, while stable pollution concentrations over time allow the use of methanol as a carbon source since the greater microbial diversity allows the elimination of other contaminants present in groundwater.

Organic carbon release, denitrification performance and microbial community of solid-phase denitrification reactors using the blends of agricultural wastes and artificial polymers for the treatment of mariculture wastewater

This paper explored the possibility of heterotrophic denitrification driven by composite solid carbon sources in low carbon/nitrogen ratio marine recirculating aquaculture wastewater. In this study, two agricultural wastes, reed straw (RS), corn cob (CC) and two artificial polymers, polycaprolactone (PCL), poly3-hydroxybutyrate-hydroxypropionate (PHBV) were mixed in a 1:1 ratio to compare the carbon release characteristics of the four composite carbon sources (RS+PCL, RS+PHBV, CC+PCL, and CC+PHBV) and their effects on improving the mariculture wastewater for denitrification. Dissolved organic carbon (DOC) after carbon source release (4.96–1.07 mg/g), total organic carbon/chemical oxygen demand (1.9–0.79) and short-chain fatty acids (SCFAs) (4.23–0.21 mg/g) showed that all the four composite solid carbon sources had excellent organic carbon release ability, and the CC+PCL group had the highest release of DOC and SCFAs. Energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used to observe the changes in the surface characteristics of the composite carbon source before and after application. And results showed that the stable internal structure enabled CC+PCL group to have continuous carbon release performance and achieved the maximum denitrification efficiency (93.32 %). The NRE results were supported by the abundance of the Proteobacteria microbial community at the phylum level and Marinobacter at the genus level. Quantitative real-time PCR (q-PCR) indicated CC-containing composite carbon source groups have good nitrate reduction ability, while PCL-containing composite carbon source groups have better nitrite reduction level. In conclusion, the carbon source for agricultural wastes and artificial polymers can be used as an economic and effective solid carbon source for denitrification and treatment of marine recirculating aquaculture wastewater.

Step-feed sequence batch reactor filled with surface-modified carriers can enhance nitrogen removal from low C/N ratio wastewater

It is difficult to achieve efficient nitrogen removal from low C/N ratio wastewater if there is no extra carbon source addition. In this study, integrated floating-film activated sludge (IFFAS) process filled with surface-modified carriers (rough, hydrophilic and positive-charged surface) was employed to enhance nitrogen removal performance. By applying step-feed sequence batch reactor strategy, high total nitrogen (TN) removal loading of 0.062 ± 0.010 kg/(m3∙d) could be achieved under the inflow flow ratio of 2:1:1 without external carbon source when treating low C/N ratio wastewater (C/N ratio: 3.5). In comparison, TN removal loading was only 0.031 ± 0.010 kg/(m3∙d) in activated sludge, and 0.057 ± 0.014 kg/(m3∙d) in IFFAS filled with conventional carrier system. The step-feed sequence batch reactor strategy resulted in complete utilization of influent carbon source for denitrification. The low C/N ratio also promoted microbial by-products production that enhanced nitrogen removal. Meanwhile, surface-modified carriers induced the mixed distribution of nitrifiers and denitrifiers. This study proposed a low-cost and efficient approach for nitrogen removal from low C/N ratio wastewater, showing potential in actual application.

Volatile fatty acids production from municipal waste streams and use as a carbon source for denitrification: The journey towards full-scale application and revealing key microbial players

Volatile fatty acids (VFAs) production is attracting interest as a sustainable approach to maximize resource recovery from organic wastes. This study explored the interlink between long-term system resilience of VFA production from primary sludge (PS) and external organic waste (OW) without pH control and the microbial community dynamics as well as the effect of substrate variability. The study elucidated the practicality of using VFA-rich effluent as a carbon source for wastewater denitrification. A 15 L bench-scale semi-continuous reactor was operated for 315 days with a feed of 70% v/v PS and 30% v/v OW and scaled up to a 2 m3 pilot-scale continuous reactor operated for 264 days. In the bench-scale study, the system was resilient with VFA production of up to 24,700 ± 400 mg COD/L and a yield of 506 ± 25 mg COD/g VSfed. The VFA composition was dominated by caproic acid up to 62% w/w. In the pilot-scale reactor, substrate variability influenced VFA production with a concentration of up to 21,500 ± 500 mg COD/L. The system was shown to be economically viable. The microbial community was dominated by Lachnospiraceae, Streptococcaceae and Comamonadaceae. The relative abundance of Lachnospiraceae gave a strong positive statistical correlation with caproic acid concentrations. The VFA-rich effluent exhibited a higher specific denitrification rate than methanol and acetate. Moreover, a continuous denitrification experiment with real nitrified wastewater resulted in a high nitrate removal efficiency with a maximum of 98%. The study demonstrates the production of bio-based products from organic wastes as alternatives to fossil-based products.

Succession dynamics of microbial communities responding to the exogenous microalgae ZM-5 and analysis of the environmental sustainability of a constructed wetland system

Constructed wetlands (CWs) are economical and effective swine tailwater treatment systems. However, nitrogen removal in CWs is limited by the lack of carbon source for denitrification. In this study, we studied the feasibility of dosing the microalgae ZM-5 to improve the nitrogen removal ability in CWs. Compared to the control CW, a 20 % higher removal capacity of COD and TN was observed for the coupled system (EG). The microalgae ZM-5 could interact with denitrifying bacteria to compensate for the deficiency of denitrifying stage in CWs. HT-qPCR chip analysis also provided evidence that denitrification genes significantly increased (p < 0.05). According to the life cycle assessment (LCA), ultrasonic extraction had the best environmental sustainability among four lipid extraction processes. As an improvement strategy, clean energy could be utilized to optimize the electricity source to reduce environmental load (45 %–60 %). These findings offer new insights into the feasibility of EG for environmentally sustainable wastewater treatment.