Abstract
The estimation of biomethane or biohydrogen yield is used to evaluate energy recovery during the process of the anaerobic treatment of waste and wastewater. Mathematically calculated theoretical values can also be used in biomethane or biohydrogen potential tests as reference points to calculate which fraction of substrate is decomposed, when the substrate degradation stopped and when the sample’s self-digestion begins. This study suggests expanded forms of equations for anaerobic processes leading to either biomethane or biohydrogen. The traditional equations describing the conversion of a substrate with known carbon, hydrogen, oxygen and nitrogen composition were expanded to account for the composition of sulfur (for biohydrogen yields) and phosphorus (both biohydrogen and biomethane yields). As an optional part, one metal cation was also incorporated into the chemical formula of the evaluated wastewater composition in case the compound of biodegradable interest exists as a salt. The equations derived here can be useful for researchers estimating energy recovery based on the elemental analysis of samples, such as algal biomass harvested during harmful algal blooms (HABs). Examples of biomethane and biohydrogen yield estimations from sulfur- and phosphorus-containing compounds are also provided.
Highlights
Biomethane and biohydrogen are two main products considered in energy recovery from waste and wastewater [1,2,3,4], which are considered to be a replacement for conventional fossil fuels [5,6,7,8]
Even though ammonia and metal hydroxide should instantly react with acidic products like aqueous carbon dioxide, hydrogen sulfide or orthophosphoric acid, it is not that clear, since the exact product depends on the strength of the acidic product, and solubility
The equation for methanogenesis including sulfur, phosphorus and one metal with defined products is: Ca Hb Oc Nd Se P f Me g + xH2 O → yCH4 + (a − y)CO2 + dNH3 + eH2 S + f H3 PO4 + gMe(OH )v
Summary
Biomethane and biohydrogen are two main products considered in energy recovery from waste and wastewater [1,2,3,4], which are considered to be a replacement for conventional fossil fuels [5,6,7,8]. No correction in a hydrogen production equation for sulfur content was found, and no studies considered both sulfur and phosphorus simultaneously for either methane or hydrogen yield Both S and P should be considered in an anaerobic process, especially when treating a mixed waste stream. With the introduction of H2 S and H3 PO4 , as final products of S and P transformation under anaerobic conditions, into Equations (1) and (2), and mineralization half-reactions [26], an ‘expanded equation’ of anaerobic fermentation, leading to the formation of either biomethane or biohydrogen, were attempted to be derived These expanded equations add both the quality and novelty to previous representations of the stoichiometry of the anaerobic digestion process, where it is important to account for sulfur- and phosphorus-containing compounds occurring in municipal and industrial wastes, with regard to evaluating the bioenergy potential for resource recovery operations
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