In-Situ Stability Control of Energy-Producing Anaerobic Biological Reactors through Novel Use of Ion Exchange Fibers Yu Tian, Arup K. SenGupta, and Derick G. Brown* Department of Civil & Environmental Engineering, Lehigh University, 1 West Packer Avenue, Bethlehem, Pennsylvania 18015, United States * S Supporting Information ABSTRACT: Anaerobic biological treatment of high-strength organic industrial wastes is preferred over aerobic treatment as it produces a methane-rich biogas, has much lower energy requirements, and produces significantly less biosolids. Process stability and reactor failure are of concern, however, for waste streams that exhibit large variations in organic loading, which can cause detrimental pH fluctuations, and that have the potential for accidental input of toxic metals. Here, we demonstrate for the first time that the use of ion exchange fibers (IXFs) can provide passive resilience to these failure modes, without requiring operator oversight or reactive process control via chemical addition. IXFs have the advantage of rapid kinetics due to their small size, and they can be readily inserted and withdrawn as woven mats or porous pillows. This approach is demonstrated here using the weak-acid IXF FIBAN X-1 and the strong-base FIBAN A-1. FIBAN X-1 passively stabilized anaerobic reactors by (i) buffering pH fluctuations resulting from organic overloading due to both an increase in organic concentration and a decrease in hydraulic residence time and (ii) moderating shock-loads of copper and nickel. FIBAN X-1 also retained ∼95% of its exchange capacity after one year of operation in anaerobic reactors, demonstrating its long-term performance. In addition, FIBAN A-1 stabilized anaerobic reactors to input of chromate. These results demonstrate that IXFs can be used to passively stabilize anaerobic biological reactors from upset and failure and that this technology can be used to enhance energy recovery from high-strength organic waste streams. KEYWORDS: Anaerobic, Ion exchange fiber, Methane, Metal toxicity, Methanogens, Organic overload ■ INTRODUCTION High-strength organic waste streams, such as those produced in agricultural, food-processing, beverage, pharmaceutical, and chemical industries, contribute to a diverse portfolio of renewable energy sources. The biological oxygen demand (BOD) of these organic wastewaters can range from 0.15 to over 100 g/L (e.g., see the Supporting Information, Table S1). Aerobic biological processes, with their proven ability to reduce BOD and their stability to upset, are commonly used to treat these industrial wastes. This treatment comes at a cost, however, with significant energy demands for the input of oxygen into the system and the production of substantial amounts of biosolids that must be dewatered and disposed. The use of anaerobic biological processes is particularly attractive for treatment of these waste streams; as anaerobic systems produce energy in the form of methane, they have much smaller operational energy requirements and are typically net energy positive, and they produce much smaller amounts of biosolids as compared to aerobic treatment (Figure 1). Anaerobic reactors also have the advantage that the BOD loading can be 5-10 times greater than that with aerobic reactors, mainly because of the inherent oxygen transfer limitations in aerobic systems. 1,2 The trade-off is that anaerobic reactors can be susceptible to operational failure due to the buildup of volatile acids, causing acidification and inhibition of methanogenesis, and the input of toxic chemicals. The key concern here is that the methanogenic archaea have low cell yields and doubling times on the order of days, compared to hours typical of aerobic microorganisms, and this can require a long recovery time after a failure. 1-3 Active operator oversight and control of these failure modes must be considered when designing and operating anaerobic systems. 2,4-14 There are many microbial processes involved in anaerobic treatment (e.g., Figure S2), and these failure modes mainly affect the final steps. Here, facultative heterotrophs produce volatile acids, which are converted to acetic acid by acetogenic bacteria. The acetic acid is then converted to methane and carbon dioxide by methanogens. The acid-forming bacteria have a higher growth rate and wider operational pH range than the methanogens. When these processes are operating at steady-state, the rate of organic acid production is balanced by the uptake rate of the methanogens, and the reactor pH is Received: July 19, 2017 Revised: September 4, 2017 Published: September 6, 2017 Research Article pubs.acs.org/journal/ascecg © XXXX American Chemical Society A DOI: 10.1021/acssuschemeng.7b02435 ACS Sustainable Chem. Eng. XXXX, XXX, XXX-XXX