Biosolids Odor Control via Peroxide Regenerated Iron –PRI-TECH® Technology

Project Scope

A field demonstration was initiated in February 2014 by the Suffolk County Department of Public Works (SCDPW) to quantify the impacts of Peroxide Regenerated Iron-Technology (PRI-TECH®) as a more economic approach in maintaining biosolids odor control in the solids handling phase at the Bergen Point Wastewater Treatment Plant (WWTP).

For approximately the last 30 years, the SCDPW Bergen Point WWTP has treated H₂S and reduced sulfur compound-based odors in the sludge handling phase at the facility with potassium permanganate (KMnO4). The sludge handling phase includes unstabilized sludge waste from three locations: sludge from the primary clarifiers; thickened waste activated sludge; and chemical sludge from the facility’s scavenger sludge collection system. The three streams are co-mingled in a 0.25 million gallon capacity sludge blend tank (SBT) that is turned over approximately every 24 hours. The blended sludge is then pumped from the SBT to belt filter presses where it is dewatered and sent via screw conveyor to trailers located outside of the solids handling building. Unstabilized sludge has many more odor causing compounds versus digested sludge so the program needed to be capable of treating odors at all stages of the solids handling operation up to and including the off-site disposal facilities.

Suffolk County explored a PRI-TECH® demonstration program in an effort to achieve equal or better performance than the historical potassium permanganate odor control program while reducing operating costs. This demonstration evaluated the use of PRI-TECH® for controlling biosolids odors, composed mainly of hydrogen sulfide gas and reduced sulfur compounds (mercaptans, etc.), while maintaining the belt filter press operation.

Technology

PRI-TECH^® is a proprietary odor control technology that utilizes iron salts and oxidants in a fashion that reduces sulfides to elementary sulfur and reduces sulfur compounds to non-odorous compounds. This program was implemented by adding ferrous chloride (FeCl₂ as the primary sulfide control agent into the primary sludge line upstream of the sludge blend tank. Hydrogen peroxide (H₂O₂ was added downstream at the sludge blend tank recirculation pumps to regenerate iron from ferrous sulfide (FeS) to either free ferrous and/or ferric iron. The H₂O² was also added to the online belt press feed pumps discharge piping to provide additional iron regeneration, oxidation of odorants and durational odor control. The iron also acts as a catalyst to allow the hydrogen peroxide to quickly and efficiently oxidize reduced sulfur compounds.

Solution

Odor control performance in their biosolids was analyzed by measuring liquid sulfide and mercaptan levels through a “shake” test in which these compounds are stripped into the vapor phase and analyzed with either OdaLog® portable gaseous hydrogen sulfide (H₂S) instruments or H₂S and RSH colorimetric tubes. In addition, H₂S was measured continuously in the headspace of the SBT with an OdaLog® vapor H₂S datalogger that had cellular transmission capability to allow for collecting data without disturbing the instrument and to allow for alarm set points to be established. Qualitative and quantitative monitoring of the dewatered biosolids trailer staging area was also performed. After program optimization during the demonstration period and ongoing operation, there were little to no recorded sulfides or mercaptans in the treated sludge from the SBT via shake test analysis. H₂S levels were statistically similar in the SBT headspace averaging 0.2 ppm with a peak of 9 ppm under PRI-TECH® operation versus an average of 0.2 ppm with a peak of 14 ppm under the prior year’s KMnO⁴ operation.

The program monitoring was expanded beyond the plant to the outside disposal sites. Analytical methods for evaluating specific odor compounds were not available at any of the disposal sites. Durational odor control was evaluated based on subjective experiences and qualitative feedback of the operators at the disposal sites. According to operators, optimization of the program, which included the use of targeted dosing profiles, produced a reduction in odors at the disposal sites.

An additional benefit of the PRI-TECH^® program is the potential to generate ferric iron (Fe₃₊) coagulant when the proper amount of H₂O2 is added, which could assist in sludge dewatering and in producing higher percent solids in the pressed filter cake. Ferric iron is generated through the reaction of ferrous iron and hydrogen peroxide. During the demonstration period and ongoing operation over the first year, polymer use rates were unaffected and an increase in percent solids was noted in the filter cake from a comparable period the previous year.

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Biosolids Odor Control via Peroxide Regenerated Iron –PRI-TECH® Technology