RECENT ADVANCEMENTS IN CHEMICAL, ENVIRONMENTAL AND ENERGY ENGINEERING Deciphering the effects of temperature on bio-methane generation through anaerobic digestion Nishat Khan 1 & Mohammad Danish Khan 1 & Suhail Sabir 1 & Abdul-Sattar Nizami 2 & Abdul Hakeem Anwer 1 & Mohammad Rehan 3 & Mohammad ZainKhan 1 Received: 16 May 2019 /Accepted: 2 December 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Anaerobic digestion (AD) is a sustainable wastewater treatment technology which facilitates energy, nutrient, and water recovery from organic wastes. The agricultural and industrial wastes are suitable substrates for the AD, as they contain a high level of biodegradable compounds. The aim of this study was to examine the AD of three different concentrations of phenol (100, 200, and 300 mg/L) containing wastewater with and without co-substrate (acetate) at four different temperatures (25, 35, 45, and 55 °C) to produce methane (CH 4 )-enriched biogas. It was observed that the chemical oxygen demand (COD) and phenol removal efficiencies of up to 76% and 72%, respectively, were achieved. The CH 4 generation was found higher in anaerobic batch reactors (ABRs) using acetate as co-substrate, with the highest yield of 189.1 μL CH 4 from 500 μL sample injected, obtained using 200 mg/L of phenol at 35 °C. The results revealed that the performance of ABR in terms of degradation efficiency, COD removal, and biogas generation was highest at 35 °C followed by 55, 45, and 25 °C indicating 35 °C to be the optimum temperature for AD of phenolic wastewater with maximum energy recovery. Scanning electron microscopy (SEM) revealed that the morphology of the anaerobic sludge depends greatly on the temperature at which the system is maintained which in turn affects the performance and degradation of toxic contaminants like phenol. It was observed that the anaerobic sludge maintained at 35 °C showed uniform channels leading to higher permeability through enhanced mass transfer to achieve higher degradation rates. However, the denser sludge as in the case of 55 °C showed lesser permeability leading to limited transfer and thus reduced treatment. Quantitative real- time PCR (qPCR) analysis revealed a more noteworthy change in the population of the microbial communities due to temper- ature than the presence of phenol with the methanogens being the dominating species at 35 °C. The findings suggest that the planned operation of the ABR could be a promising choice for CH 4 -enriched biogas and COD removal from phenolic wastewater. Keywords Biodegradability . Methanogens . Mesophiles . Acidogenesis . Renewable energy Introduction The environmental pollution caused by chemicals is an alarming issue in all parts of the world (Zhang et al. 2011). Environmental Protection Agency (EPA) lists phenol as one of the most dangerous pollutant chemicals, which is released by different industries including chemical, textiles, pesticides, pharmaceutics, and petroleum (Keith and Telliard 1979). It is also used in various applications like manufacturing of phe- nolic, epoxy, polyamide, and polycarbonate resins (Manojlovic et al. 2007). The discharge of phenol into the environment creates severe issues due to its toxic and carci- nogenic nature (Ahmad et al. 2012). The environmental pro- tection laws direct to various phenol treatment techniques to restrict its release into the environment (Lefèvre et al. 2011) Responsible editor: Ta Yeong Wu Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-019-07245-w) contains supplementary material, which is available to authorized users. * Abdul-Sattar Nizami nizami_pk@yahoo.com * Mohammad ZainKhan dr_mzain.fa@amu.ac.in 1 Department of Chemistry, Environmental Research Laboratory, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India 2 Sustainable Development Study Centre, Government College University, Lahore, Pakistan 3 Center of Excellence in Environmental Studies (CEES), King Abdulaziz University, Jeddah, Saudi Arabia Environmental Science and Pollution Research https://doi.org/10.1007/s11356-019-07245-w