Addressing Biosolids Hydrogen Sulfide Odor Complaints While Meeting Effluent Metals Limits--A Win-Win for a Brewery

ABSTRACT A brewery wastewater treatment plant (WWTP) experienced high hydrogen sulfide (H2S) concentrations in and around the biosolids handling building which led to concerns around worker safety, overloading of the existing odor scrubber, and odor complaints from the surrounding neighborhoods. The Brewery WWTP dewaters a total of 250,000 300,000 gallons per day of mixed primary and waste activated sludge (biosolids). Of the total flow to the dewatering presses, 80% is from the brewery and the remaining 20% from a nearby municipal wastewater treatment plant. Historically, the brewery fed sodium permanganate ahead of the belt filter press in an effort to reduce H2S odors in and around the biosolids dewatering area. A second permanganate dosing point of was added in 2021 to address the continued odor complaints. Later in 2021, both permanganate injection points were decommissioned due to operational concerns. Permanganate was also suspected of contributing to elevated manganese levels at the effluent due to release of manganese in the filtrate. In early 2022, the brewery WWTP embarked on a 90-day field trial of Peroxide Regenerated Iron Technology (PRI-TECH ®) to address H2S odors generated in the biosolids dewatering facility and also eliminate a source of manganese in the final effluent. For H2S control, PRI-TECH ® functions in two ways: 1) Direct oxidation of H2S by hydrogen peroxide (H2O2) and 2) regeneration of bound iron (e.g, FeS) in-situ, yielding either free ferrous (Fe2+) or ferric (Fe3+) iron and colloidal sulfur. This regenerated iron is now available to bind additional H2S in the biosolids handling process, functioning the same as if fresh iron salts were being added. Pre-trial laboratory testing showed that there were already significant levels of total available iron present in the brewery biosolids (15 25 mg/L total Fe). This equates to 35 40 lbs. per day of iron that was available for regeneration. In this case, the iron needed for PRI-TECH ® was already present in the biosolids and could be used for the benefit of H2S control in the belt filter press area. For the PRI-TECH ® trial, hydrogen peroxide was fed into the combined biosolids line upstream of the belt filter presses to oxidize H2S and regenerate free iron (Fe+2, Fe+3). Baseline (untreated) H2S levels at the belt press ranged from 5 90 ppm with an average above 10 ppm. The brewery safety committee set the H2S compliance target below an average of 10 ppm during dewatering operations to ensure worker safety and to reduce complaints from surrounding neighborhoods. Trial results showed that PRI-TECH ® reduced the sulfide levels by >95% with operational vapor level averages <1ppm inside the belt filter press room. Operations noticed a substantial reduction in local and personal H2S alarms (alarm at 10 ppm) in and around the dewatering building, local odor complaints also decreased, and there were no effluent manganese violations since beginning the PRI-TECH ® program, supporting compliance with metal discharge limits. Based on the successful trial results, the brewery WWTP will continue utilizing PRI-TECH ® to maintain effective H2S control in the dewatering facility to ensure worker safety and maintain effective H2S odor. Future work is planned to further optimize PRI-TECH ® program, with additional investigation into the improvement in critical metals reduction.