The study was conducted to demonstrate the influence of extracellular secretions from Microbacterium on the reductive dechlorination of tetrachloroethene (PCE). A series of mixed cultures were established from a paddy soil sample. In the mixed cultures amended with extracellular secretions from Microbacterium, PCE was rapidly and completely converted into cis-1,2-dichloroethene (cis-DCE) and trans-1,2-dichloroethene (trans-DCE) within 40 days. The unamended mixed cultures showed weak signs of dechlorination after a pronounced lag phase, and trichloroethene (TCE) was accumulated as a major end product. This result means that amendment with extracellular secretions from Microbacterium shortened the lag phase, increased the dechlorination velocity and promoted the production of less-chlorinated chloroethene. The results were corroborated by defined subculture experiments, which proved that microorganisms from unamended mixed cultures could also be stimulated by extracellular secretions from Microbacterium. Desulfitobacterium was identified as the main dechlorinating population in all mixed cultures by direct PCR. Additionally, the 16S rRNA gene copies of Desulfitobacterium increased by one or two orders of magnitude with PCE dechlorination, which provided corroborative evidence for the identification result. The volatile fatty acids were monitored, and most interestingly, a close association between propionate oxidation and dechlorination was found, which has rarely been mentioned before. It was assumed that the oxidation of propionate provided hydrogen for dechlorination, while dechlorination facilitated the shift of the reaction toward propionate oxidation by reducing the partial pressure of hydrogen.

The bio-reduction of hexavalent chromium (Cr(VI)) by anaerobic fermentation is considered as a promising, low-cost and environment-friendly way. However, it is unclear for the reduction mechanisms of Cr(VI) in an anaerobic hydrogen fermenter, such as reduction kinetics, related electron donors, migration and transformation, reduction site and key components, and related microorganisms. To clarify these issues, a hydrogen fermenter was designed to reduce Cr(VI) at 55 °C with glucose as initial substrate. Results show that 100 mg/L Cr(VI) can be completely reduced (99.5%) to trivalent chromium (Cr(III) through chemical and biological reactions. Bio-reduction dominates Cr(VI) removal in a first-order exponential decay mode with both glucose and its metabolites (volatile fatty acids) as electron donors. Moreover, volatile fatty acids are more suitable as electron donors for Cr(VI) bio-reduction than glucose. Bacilli, Clostridia and Thermotogae in the fermenter dominated the reduction of Cr(VI) by regulating the production and composition of extracellular polymers (EPSs), in which carboxyl and hydroxyl groups play an important role for Cr(VI) reduction by coordination. The results can guide us to regulate the bio-reduction of Cr(VI), and provide reference for the development of bio-reduction technology of Cr(VI).

Rumen liquid can effectively degrade lignocellulosic biomass, in which rumen microorganisms play an important role. In this study, transformation of bacterial community structure in rumen liquid anaerobic digestion of rice straw was explored. Results showed that rice straw was efficiently hydrolyzed and acidified, and the degradation efficiency of cellulose, hemicellulose and lignin reached 46.2%, 60.4%, and 12.9%, respectively. The concentration of soluble chemical oxygen demand (SCOD) and total volatile fatty acid (VFA) reached 12.9 and 8.04 g L⁻¹. The high-throughput sequencing results showed that structure of rumen bacterial community significantly changed in anaerobic digestion. The Shannon diversity index showed that rumen bacterial diversity decreased by 32.8% on the 5th day of anaerobic digestion. The relative abundance of Prevotella and Fibrobacter significantly increased, while Ruminococcus significantly decreased at the genus level. The Spearman correlation heatmap showed that pH and VFA were the critical factors affecting the rumen bacterial community structure. The function prediction found that rumen bacteria mainly functioned in carbohydrate transport and metabolism, which might contain a large number of lignocellulose degrading enzyme genes. These studies are conducive to the better application of rumen microorganisms in the degradation of lignocellulosic biomass.

Converting biowaste into value-added products has raised the researchers’ interests. In this study, bioconversion was applied to produce chain acids from food waste by anaerobic fermentation. To improve the caproic acid production, different pretreatments (i.e., ultrasonic, hydrothermal, and alkaline-thermal) were used for investigating their effects on the acidogenic production and microbial communities. The results showed that ultrasonic and hydrothermal pretreatments (207.8 and 210.1 mg COD/g VS, respectively) were very efficient for enhancing the caproic acid production, compared to the alkaline-thermal pretreated samples and control samples (72.6 and 97.5 mg COD/g VS, respectively). The ultrasonic pretreatment was beneficial for reducing volatile fatty acids (VFAs) during the caproic acid production, resulting in converting more lactic acid to caproic acid by adding the hydrothermal pretreatment. The microbial community analysis showed that the acidogenic bacteria Caproiciproducens dominated the fermentation in this bioconversion process of food waste into chain acids. The Caproiciproducens mainly degraded the proteins and carbohydrates from the saccharified residues of food waste to produce caproic acids through chain elongation procedure. The investigation and optimized method may help develop the bioconversion technology for producing VFAs products from food wastes.

This study lays great emphasis on establishing a reliable analytical platform to quantify and specify volatile fatty acids (VFAs) in the aqueous phase by derivatizing VFAs into their corresponding alkyl esters via thermally-induced rapid esterification (only 10 s reaction time). To this end, reaction conditions for the thermally-induced rapid esterification are optimized. A volumetric ratio of 0.5 at 400 °C for VFA/methanol is identified as the optimal reaction conditions to give ∼90% volatile fatty acid methyl ester (VFAME) yield. To maintain a high yield of VFAMEs, this study suggests that dilution of the sample to an optimum concentration (∼500 ppm for each VFA) is required. Derivatization of VFAs into VFAMEs via the thermally-induced rapid esterification is more reliable to quantify and specify VFAs in the aqueous phase than conventional colorimetric method.

In agricultural lowland landscapes, intensive agricultural is accompanied by a wide use of agrochemical application, like pesticides and fertilizers. The latter often causes serious environmental threats such as N compounds leaching and surface water eutrophication; additionally, since perchlorate can be present as impurities in many fertilizers, the potential presence of perchlorates and their by-products like chlorates and chlorites in shallow groundwater could be a reason of concern. In this light, the present manuscript reports the first temporal and spatial variation of chlorates, chlorites and major anions concentrations in the shallow unconfined aquifer belonging to Ferrara province (in the Po River plain). The study was made in 56 different locations to obtain insight on groundwater chemical composition and its sediment matrix interactions.During the monitoring period from 2010 to 2011, in June 2011 a nonpoint pollution of chlorates was found in the shallow unconfined aquifer belonging to Ferrara province. Detected chlorates concentrations ranged between 0.01 and 38 mg/l with an average value of 2.9 mg/l. Chlorates were found in 49 wells out of 56 and in all types of lithology constituting the shallow aquifer. Chlorates concentrations appeared to be linked to NO3−, volatile fatty acids (VFA) and oxygen reduction potential (ORP) variations. Chlorates behaviour was related to the biodegradation of perchlorates, since perchlorates are favourable electron acceptors for the oxidation of labile dissolved organic carbon (DOC) in groundwater. Further studies must take into consideration to monitor ClO4− in pore waters and groundwater to better elucidate the mass flux of ClO4− in shallow aquifers belonging to agricultural landscapes.

Constructed wetlands (CWs) can be used for tertiary treatment of wastewater; however, carbon source shortages limit denitrification. We studied the effect of algae addition as an external carbon source in CWs and found that the nitrogen removal efficiency of CWs is highly dependent on the algae dosage. Optimal nitrogen removal percentage (80.5%) can be achieved by adding 81.1 mg·L⁻¹ dry weight algae to the influent when the chemical oxygen demand/nitrogen (COD/N) ratio reaches 5.3. Longitudinal changes in the nitrogen concentrations, organic matter concentrations, and nitrogen functional genes were also analyzed. The algae addition strengthened the anoxic environment, boosted the volatile fatty acid concentrations, and improved the ratio of nitrite reductase gene (nirS) and copper-containing nitrite reductase (nirK)/16S rRNA, as well as the ratio of nitrate reductase gene (narG)/16S rRNA, thereby expanding the active space for denitrification. The addition of algae could potentially provide enough carbon to enhance denitrification during treatment of wastewater with a low COD/N ratio.

Polybrominated diphenyl ethers (PBDEs) widely existing in the environment can pose a serious threat to the ecological safety. However, the influence of PBDEs on methane production by excess sludge (ES) and kitchen waste (KW) anaerobic co-digestion and its mechanism is not clear. To fill this gap, in this work, the co-digestion characteristics of ES and KW exposed to different levels of PBDEs at medium temperature were investigated in sequencing batch reactor, and the related mechanisms were also revealed. The results showed that PBDEs reduced methane production and the proportion of methane in the biogas. Methane yield decreased from 215.3 mL/g· volatile suspended solids (VSS) to 161.5 mL/(g·VSS), accompanied by the increase of PBDE content from 0 to 8.0 mg/Kg. Volatile fatty acid (VFA) yield was also inhibited by PBDEs; especially when PBDEs were 8.0 mg/Kg, VFA production was only 215.6 mg/g VSS, accounting for 75.7% of that in the control. Mechanism investigation revealed PBDEs significantly inhibited the processes of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Further study showed that PBDEs could inhibit the degradation and bioavailability of ES and KW, but it had a greater inhibition on the utilization of KW. Enzyme activity investigation revealed that all the key enzyme activities related to methane production were suppressed by PBDEs.

Anaerobic digestion is a possibility for post-hydrothermal liquefaction wastewater (PHWW) treatment because this wastewater is rich in nutrients and organic compounds. However, the PHWW presents many toxic compounds. A strategy for the anaerobic treatment of toxic compounds is using biomass adhered to inert supports forming biofilms, which can offer more resistance to the microorganism and protection from such compounds. The continuous treatment of PHWW is the essential key to obtaining a sustainable hydrothermal liquefaction process. In this work, the use of immobilized biomass was evaluated for the anaerobic degradation of PHWW from Spirulina in batch assays and continuous treatment. Higher methane production potential and volatile fatty acid mass balance showed the advantages of using biomass immobilized in polyurethane foam. Continuous treatment in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor reached chemical organic demand (COD) removal efficiencies of 67% and 58% for volumetric organic load rates of 0.8 and 1.6 g COD.L⁻¹.d⁻¹, respectively. After 200 days of continuous treatment, Anaerobaculum and Coprothermobacter, fermentative proteolytic genera of bacteria with potential for hydrogen production, were favored.