Sweetmeat waste fractions as suitable organic carbon source for biological sulfate reduction

• Sweetmeat waste was characterized for biological sulfate reduction.
• High sugar with diverse organic acids present in the waste.
• Filtered fraction showed best result, using raw resulted sulfate reduction inhibition.
• Supplement of external nitrogen to balance C:N is considered necessary with time.

Characterization of commonly available sweetmeat waste (SMW) was carried out to encourage controlled biological sulfate reduction. SMW was found to be mild acidic semisolid waste material that contains high sugar (520–580 mg g−1) and reasonable amount of utilizable organic acids for sulfate reducing bacteria (SRB). Various fractions of SMW at different concentrations were tested for usefulness to support SRB growth and sulfate reduction. Most fractions worked well in lower concentrations (COD: SO42−SO42− around 1.2) with balanced bacto-tryptone supplement (C:N ∼11). Raw SMW was not as useful to SRB; however, filtered SMW fraction was found the most acceptable in terms of sulfate reduction (70%) – comparable to 90% reduction by pure lactate supplement. All SMW fractions supplemented media encouraged reasonable bacterial population (106–107 cells ml−1). Dominance of SRB population in filtered SMW fraction (up to 93.5% of total population) among all fractions was observed by fluorescence in situ hybridization (FISH) study. Desulfovibrio desulfuricans was found to be the common SRB species in all fractioned media. Results showed that designed and regulated sweetmeat waste can be used as a proper substitute of commercially available organic carbon sources, in terms of biological sulfate reduction. Such findings point toward the prospects of commercial use of amply available SMW, hither to unreported in the literature.