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Fate and removal of organic pollutants, recalcitrant nutrients, and antimicrobials during single-stage and sequential sludge digestion.

University of British Columbia

Digestion of biological nutrient removal (BNR) sludge can be difficult due to the release of nutrients in sludge dewatering liquids/centrate which can lead to performance issues and discharge limit exceedances if not carefully managed. This can be particularly challenging for small to medium wastewater treatment facilities (WWTF) which often lack the scale, and/or technical expertise required to make many existing sludge digestion technologies feasible. Furthermore, trace micropollutants including the ubiquitous antimicrobials triclosan (TCS) and triclocarban (TCC) remaining in digested sludge can increase public opposition to, and further complicate, biosolids reuse and/or disposal. The objective of this study was to compare the impact of various types of sludge digestion, sludge retention times (SRTs) and temperatures on mixed primary and secondary BNR sludge for small-to medium-sized WWTFs. Conventional mesophilic anaerobic digestion (AD), cycling aerobic/anoxic digestion (AERO/ANOX), and sequential anaerobic/aerobic/anoxic digestion (AD/AERO/ANOX) at both room (22°C) and mesophilic (35°C) temperatures were compared at SRTs ranging from 5 to 20-days against the existing no-digestion baseline scenario. Conventional AD and sequential AD/AERO/ANOX digesters with a mesophilic second-stage were the most effective in reducing solids for disposal, removing up to 47.4 ± 1.4% and 51.7 ± 4.4% of total solids from digester feed, respectively. AERO/ANOX was very effective in treating recalcitrant forms of nitrogen and phosphorous by removing up to 99.0% of dissolved organic nitrogen (DON), and up to 88.4 ± 5.3% of non-reactive dissolved phosphorous (NRDP) from the digester feed. This can achieve nutrient levels that are lower than existing baseline (without sludge digestion) and may even improve BNR facility effluent quality. Single-stage AERO/ANOX digesters were the most effective against antimicrobials, yielding up to an 80.3 ± 2.5% TCS removal from undigested sludge. The second-stage of the sequential AD/AERO/ANOX digesters also showed significant improvements in TCS removals with a 24.0 ± 4.2% improvement in TCS removal from the first AD stage and up to 48.6 ± 3.0% removal overall. These results have significant practical implications as an increasing number of small to medium WWTFs look for biosolid management solutions while employing BNR processes to meet evermore-stringent nutrient and future micropollutant discharge limits.

Text

2020-07-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/75281

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/