The detailed emission of different gaseous pollutants along with characteristics and environmental impacts from direct burning of valuable wastes have been reported by (Iqbal et al., 2019). In addition, various studies have revealed that biomass residue carries promising potential of alternative energy generation owing to its carbon neutral nature, low prices, and abundant availability. These pros have attracted scientists’ attention towards use of biomaterial for generation of clean energy as renewable energy to meet growing energy demands and preservation of the environment (Javed et al., 2016). Among the renewable energies, biogas has advantage that it is not a fluctuating source. Biogas can be gained in an anaerobic digestion process from different organic substances. There are over 7 billion people in the world with a fecal output of 1–2 kg/person/day, equating to 7–14 million tons of fecal waste generated on a daily basis (Fagbohungbe et al 2015). This is an enormous amount of energy that could be generated if the human fecal material (HFM) was used as a feedstock for driving anaerobic digestion (AD). More recently, the use of HFM as a feedstock for AD has continued to increase, particularly in developing countries (Fagbohungbe et al 2015). Currently, in Dar es Salaam -Tanzania has a limited number of fecal sludge treatment sites that officially allow the discharge of. There are nine existing water stabilization ponds (WSPs): Vingunguti, Kurasini, Mikocheni, Lugalo, University of Dar es Salaam, Mabibo, Buguruni, Ukonga Prison, and one at the Airwing. Of these only two receive FS: Vingunguti and Kurasini. These ponds have been underperforming since their design capacities are no longer able to cater to the current population’s demands. The level of maintenance for the WSPs is very low, which leads to poor performance of the facilities (DAWASA, 2020). The utilization fecal sludge as a potential feedstock for AD massive potential as a renewable energy source in Tanzania as a developing country. Biochar, a combustible carbon-rich solid material produced via gasification or pyrolysis of biomass wastes (Cho et al., 2017), has been touted as a promising additive with many desirable characteristics for enhancing the AD process (Faghohungbe et al., 2017, Mumme et al., 2014). In particular, biochar’s porous structure serves as a good immobilization matrix for enhanced bacterial and methanogens growth in the AD digesters, which leads to higher methane yields (Faghohungbe et al., 2017). Additionally, biochar as a conductive material promotes direct interspecies electron transfer (DIET) between methanogens and exoelectrogenic bacteria in the AD digesters (Park et al., 2018, Wang et al., 2019). Biochar also mitigated double inhibition risk from both ammonia and acids by firstly enriching Methanosaeta and then Methanosarcina (Lu et al., 2016). Due to its high surface area and resultant high adsorption capability, biochar is known to adsorb heavy metals (Inyang et al., 2011, Gan et al., 2018), phosphate (Yao et al., 2011), and other inhibitive organic compounds like volatile fatty acids (VFAs) (Faghohungbe et al., 2017). Moreover, biochar improved digester buffering capacity and reduced acidification by affecting the alkalinity of the digester (Sunyoto et al., 2016, Pan et al., 2019), and improved the granulation of anaerobic sludge (Wang et al., 2018) and the fertilizer utilization of the digestate (Zhang et al., 2019). Furthermore, the pre-treatment would make the biochar have a larger specific surface area and better adsorption performance (Rajapaksha et al., 2016).
Therefore, the aim of this study was to evaluate the effect biochar particle size as supplement materials for anaerobic digestion as a treatment option of fecal sludge. The process performance was assessed by measuring methane content, methane volume, pH, Total and Volatile solid removal as well as Chemical oxygen removal.