The growing inequality between firms

Globalisation, technological progress and a range of policies and institutions are driving ‘Great Divergences’ in wages and productivity, write Giuseppe Berlingieri, Patrick Blanchenay and Chiara Criscuol

Hydrogen Recovery from Waste Activated Sludge: Role of Free Nitrous Acid in a Prefermentation–Microbial Electrolysis Cells System

Due to the limited hydrolysis rate of particulate organics and suitable substrates for hydrogen-producing bacteria in raw waste activated sludge (WAS), traditional fermentative hydrogen production has low hydrogen yield and energy recovery efficiency. The role of free nitrous acid (FNA) pretreatment on WAS and hydrogen recovery was investigated in a prefermentation–microbial electrolysis cells (MECs) system. The results demonstrated that WAS hydrolysis and acidification were enhanced by FNA pretreatment. Notably, the accumulation of acetic acid and propionic acid eventually reached to 55% and 22% during prefermentation. During MECs cascade utilization, volatile fatty acids (VFAs) were exhausted and the utilization efficiencies of soluble carbohydrates and proteins reached 62% and 41.5%, respectively. The hydrogen yield from FNA-pretreated sludge was 1.44 mL/g of volatile suspended solids, which was approximately 3 times than that of the control. High-throughput sequencing and canonical correspondence analysis revealed that FNA pretreatment promoted the hydrolysis and acidification of particulate organics, through accumulating anaerobic fermentation bacteria in prefermentation, and, furthermore, stimulated the increase of electrochemically active bacteria, thereby enhancing the current and hydrogen production. This study may provide a sound basis for the potential implementation of FNA pretreatment to accomplish cascading utilization of organics and the synchronous recovery of energy from WAS

Biocathodic Methanogenic Community in an Integrated Anaerobic Digestion and Microbial Electrolysis System for Enhancement of Methane Production from Waste Sludge

Understanding the microbial community structure relative to enhancement of methane production from digestion of waste-activated sludge (WAS) coupled with a bioelectrochemical system is a key scientific question for the potential application of bioelectrochemistry in biogas production. Little has been known about the influence of electrode on the structure and function of microbial communities, especially methanogens in a bioelectrochemical anaerobic digestion (AD) reactor. Here, a hybrid reactor, which coupled bioelectrolysis and AD, was developed to enhance methane recovery from WAS. The methane production rate reached up to 0.0564 m³ methane/(m³ reactor*d) in the hybrid reactor at room temperature, which was nearly double than that of the control anaerobic reactor (0.0259 m³ methane/(m³reactor*d)) without bioelectrochemical device. Microbial community analysis revealed that hydrogenotrophic methanogen <i>Methanobacterium</i> dominated the cathode biofilm, which was the predominant contributor to accelerate the methane production rate from WAS. While acetoclastic methanogen <i>Methanosaeta</i> was enriched in the sludge phase of all reactors, shifts of the microbial community structure of the biocathode was in significant correlation with the methane production. This study suggested a potential way to utilize a bioelectrochemical system with the regulated microbial community to enhance methane production from WAS