Effect of various pretreatment methods on anaerobic mixed microflora to enhance biohydrogen production utilizing dairy wastewater as substrate

Abstract

Influence of different pretreatment methods applied on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H₂) producing mixed culture using dairy wastewater as substrate. The experimental data showed the feasibility of molecular biohydrogen generation utilizing dairy wastewater as primary carbon source through metabolic participation. However, the efficiency of H₂ evolution and substrate removal efficiency were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. Among the studied pretreatment methods, chemical pretreatment (2-bromoethane sulphonic acid sodium salt (0.2 g/l); 24 h) procedure enabled higher H₂ yield along with concurrent substrate removal efficiency. On the contrary, heat-shock pretreatment (100 °C; 1 h) procedure resulted in relatively low H₂ yield. Compared to control experiments all the adopted pretreatment methods documented higher H₂ generation efficiency. In the case of combination experiments, integration of pH (pH 3; adjusted with ortho-phosphoric acid; 24 h) and chemical pretreatment evidenced higher H₂ production. Data envelopment analysis (DEA), a frontier analysis technique model was successfully applied to enumerate the relative efficiency of different pretreatment methods studied by considered pretreatment procedures as input and cumulative H₂ production rate and substrate degradation rate as corresponding two outputs.

Introduction

With increasing gap between the energy requirement of the industrialized world and inability to replenish such needs from the limited sources of energy like fossil fuels, an ever increasing levels of green house pollution from the combustion of fossil fuels in turn aggravate the perils of global warming and energy crisis. Hydrogen (H₂) is a promising green alternative to fossil fuels as a sustainable energy source with minimal or zero use of hydrocarbons and high-energy yield (122 kJ/g) (Mu et al., 2006). Availability of abundant amount of wastewater coupled with acidophilic anaerobic treatment resulting in H₂ generation is considered to be an ideal methodology to reduce pollution load apart from renewable energy generation. Recently international support for developing these relatively new sources of energy was increased due to their benefits one such benefit is the reduction in green house gas emissions (Chynoweth et al., 2001, Charters, 2001, Logan, 2004). H₂ generation during anaerobic wastewater treatment involves hydrolysis, acidogenesis and solventogenesis of which hydrolysis is the rate limiting step (Li and Noike, 1992). At present a practical and efficient H₂ generation process is the growing concern among the research fraternity (Logan, 2004, Hawkes et al., 2002). Pretreatment of parent anaerobic inoculum is one strategy which helps to accelerate the hydrolysis step reducing the impact of rate limiting step and augment the anaerobic digestion to enhance H₂ generation (Kim et al., 2003, Zhu and Béland, 2006). Thermal pretreatment, alkaline pretreatment, acidification, ultrasonic pretreatment, etc., are a few pretreatment methods employed to enhance H₂ production (Woodard and Wukasch, 1994, Sawayama et al., 1996, Penaud et al., 1999, Zhu and Béland, 2006). In this study we have made an attempt, to evaluate the efficiency of different pretreatment methods on anaerobic mixed microflora for selectively enriching H₂ producing mixed consortia to enhance biohydrogen evolution rate and substrate removal efficiency utilizing diary wastewater as main substrate.