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This work developed an adsorptive separation and recovery process for anaerobically generated volatile fatty acids (VFAs) from swine wastewater fermentation. Batch adsorption studies were conducted using several weak anion exchange resins and synthetic adsorbent resins to identify a suitable candidate. Relite RAM2 with a tertiary amine functional group showed the highest adsorption (over 98%) of hexanoic acid. Under the different pH values (1.8–7.5) and extraction temperatures (30–50 °C), the highest adsorption was observed at a pH of 3.2, which is below the pKa of hexanoic acid, at all the evaluated temperatures. A full factorial design was used to optimize the resin and VFA concentrations, wherein over 99% adsorption could be achieved when the ratio of VFA to resin was below 0.23 (g/g) for model solution (VFAs in water). The adsorption equilibrium could be achieved within 30 min of contact time and 0.5% w/v NaOH was identified as a suitable desorption agent. Under the optimal conditions, 65–72% of VFAs present in fermentation broth was adsorbed, which was increased to 72–76% by using fresh resins. The VFAs adsorption and recovery efficiency were maintained for 9 successive cycles without requiring extensive resin washing and regeneration for both model solution and fermentation broth. Overall, the work presents a comprehensive study for resin adsorption to recover VFAs and provides a potential industrial-relevant process to recover VFAs from fermentation broth.

Pollution from animal wastes is a threat to water resources. Insufficient treatment and disposal of animal manure results in potential runoff and transport of waste into surface and groundwater and ultimately contaminating drinking water in many rural areas. The goal of this research is to assess the efficiency of an innovative configuration of anaerobic membrane bioreactor (AnMBR) and constructed wetlands (CWs) to treat animal waste, providing a sustainable, resilient management system for agricultural wastewaters. Numerical simulations were conducted to assess the capacity of CWs to remove nutrients from AnMBR permeate with varying ammonium (NH4+), phosphorus (P), and chemical oxygen demand (COD) concentrations and temperature conditions (10°C, 20°C, 30°C, and 40°C). The simulations were conducted using HYDRUS software with the Constructed Wetland 2D (CW2D) module. The results supported the assumption that CWs can be an efficient polishing step for AnMBR permeate, removing more than 90% of NH4+ and P, which was further confirmed with experimental measurements. The effectiveness of this design relies on the natural processes for nutrient removal that can be optimized by altering nutrient and COD loading rates from the AnMBR system. When AnMBR systems face unexpected failures or technical issues, the integration of CWs provides a reliable contingency plan, ensuring a practical and resilient wastewater treatment process. The findings from this research offer significant promise for developing cost-effective and environmentally friendly solutions for the treatment and reuse of concentrated animal feeding operations (CAFOs) wastewater through a hybrid treatment configuration, contributing to the broader goals of decentralized wastewater treatment and agricultural practices. [ABSTRACT FROM AUTHOR]

Abstract Background Buffering to achieve pH control is crucial for successful trichloroethene (TCE) anaerobic bioremediation. Bicarbonate (HCO3−) is the natural buffer in groundwater and the buffer of choice in the laboratory and at contaminated sites undergoing biological treatment with organohalide respiring microorganisms. However, HCO3− also serves as the electron acceptor for hydrogenotrophic methanogens and hydrogenotrophic homoacetogens, two microbial groups competing with organohalide respirers for hydrogen (H2). We studied the effect of HCO3− as a buffering agent and the effect of HCO3−-consuming reactions in a range of concentrations (2.5-30 mM) with an initial pH of 7.5 in H2-fed TCE reductively dechlorinating communities containing Dehalococcoides, hydrogenotrophic methanogens, and hydrogenotrophic homoacetogens. Results Rate differences in TCE dechlorination were observed as a result of added varying HCO3− concentrations due to H2-fed electrons channeled towards methanogenesis and homoacetogenesis and pH increases (up to 8.7) from biological HCO3− consumption. Significantly faster dechlorination rates were noted at all HCO3− concentrations tested when the pH buffering was improved by providing 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as an additional buffer. Electron balances and quantitative PCR revealed that methanogenesis was the main electron sink when the initial HCO3− concentrations were 2.5 and 5 mM, while homoacetogenesis was the dominant process and sink when 10 and 30 mM HCO3− were provided initially. Conclusions Our study reveals that HCO3− is an important variable for bioremediation of chloroethenes as it has a prominent role as an electron acceptor for methanogenesis and homoacetogenesis. It also illustrates the changes in rates and extent of reductive dechlorination resulting from the combined effect of electron donor competition stimulated by HCO3− and the changes in pH exerted by methanogens and homoacetogens.