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Effects of metal salts on odour, pathogens, dewaterability and orthophosphate during the anaerobic digestion of municipal waste sludge

University of British Columbia

This research explores the effects of using common metal salts to address some of the barriers to the wider adoption of anaerobic digestion (AD), which include the generation of corrosive and odourous volatile sulfur compounds (VSCs), pathogens remaining in the digestate, along with the re-release nutrients from the digested solids. The effects of chemical addition were studied by adding two different doses of ferric chloride (FC), aluminum sulfate (alum) (AL) and magnesium hydroxide (MG) to the feed of seven lab-scale semi-continuously fed anaerobic digesters. Digesters were operated at mesophilic temperatures (35 ± 2°C) at three different sludge retention times (SRTs) of 20, 12, and 7 days over a one-year period to assess the impacts of dosing on the aforementioned barriers to AD along with the effects of dosing on dewaterability of digested sludge and AD performance and stability. Both doses of FC were very effective in reducing VSCs by up to 87% versus an undosed (control) digester. Both doses of AL increased VSC levels significantly, with the higher dose increasing VSC levels to levels which are extremely dangerous to people and property. Neither level of MG addition had a statistically significant effect on VSCs. The effects of FC on pathogens were mixed with the lower dose showing a modest reduction in pathogens while the higher dose had the opposite effect. Both levels of AL were highly effective in reducing pathogens by up to 86% and may be a valuable tool pathogen reduction targets. Both levels of MG were shown to increase levels of total coliforms and E-coli in digested sludge. FC was far more effective in reducing nutrients in AD effluent versus the control and reduced soluble orthophosphate by nearly 61%. AL was even more effective achieving a near 70% reduction in orthophosphate, while MG had little effect on orthophosphate. None of the compounds appeared to have a significant adverse effect on AD operation at lower organic loading rates, although AL caused digester instability at higher doses and organic loading rates. Neither dose of any of the compounds had a statistically significant effect on sludge dewaterability.

Text

2014-12-23

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/51657

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/