Acid Mine Drainage Treatment Case Study

USP-OC31TM, CHLORITE OXIDANT BLEND, FOR SULFIDE AND ORGANIC ODOR CONTROL

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Introduction

USP-OC31 is a chlorite-based oxidant blend that is designed to efficiently and rapidly oxidize hydrogen sulfide and organic odors in wastewater collection systems, treatment plants (headworks, thickeners, dewatering operations) and industrial wastewaters. USP-OC31 is environmentally friendly and does not form chlorinated by-products, with the end-product being table salt (sodium chloride).

USP-OC31 Properties & Dosing

USP-OC31’s main active ingredient, sodium chlorite (NaClO2), is a fast-reacting oxidant (seconds) that provides immediate control of hydrogen sulfide and many other organic odors in collection systems, treatment plants and industrial wastewaters, particularly in solids processing operations. Unlike hypochlorite, USP-OC31 does not react with ammonia and does not form chlorinated organics. USP- OC31 oxidizes hydrogen sulfide according to the following equation…

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PRI-SC® PEROXIDE REGENERATED IRON – SULFIDE CONTROL

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Introduction

Sulfide odor control within sanitary sewers has been practiced for over 50 years, yet only recently have substantive advances been made. Where once the choice of chemical treatment was either chlorine or iron salts, safer and more environmentally benign technologies based on hydrogen peroxide, nitrates and/or magnesium hydroxide have gained acceptance. These new alternatives, however, can increase treatment costs substantially and present limitations in themselves. USP Technologies identified and addressed this issue by lessening the adverse impacts of the older, cheaper mainstays, particularly iron salts such as ferrous/ferric chloride or sulfate that provide other benefits to wastewater treatment operations.

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PERACETIC ACID FOR MUNICIPAL WASTEWATER DISINFECTION

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Introduction

Peracetic Acid (PAA) is an organic peroxide compound with the formula CH3CO3H. It is environmentally friendly as it hydrolyzes to acetic acid and hydrogen peroxide in water. It is a broad-spectrum biocide with a fast reaction time in minutes and leaves no harmful by-products.

Peracetic acid is a strong oxidant and disinfectant with oxidation potential higher than that of chlorine or chlorine dioxide. PAA is available in the form of equilibrium mixture which also contains hydrogen peroxide, acetic acid (vinegar) and water as shown by the following equation…

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DRINKING WATER TREATMENT – HYDROGEN PEROXIDE PRE-OXIDANT APPLICATION

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Introduction

The use of hydrogen peroxide (H2O2) as a pre-oxidant in municipal water treatment is well documented and has been practiced for over 15 years. Historical applications of H2O2 in drinking water have been for taste and odor control, hydrogen sulfide removal, iron removal and ozone enhancement/destruction. With the EPA Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) coming into effect, more recent emphasis has been on the reduction of the formation of total trihalomethanes (TTHM) and haloacetic acids (HAA5).

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CLOEVIS BIOFILM REMOVAL SERVICE

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Cloevis Biofilm Removal Service (Cloevis BRS) is an innovative technology offering that removes the biofilms that adhere to the inner surfaces of wastewater forcemain walls, including the underlying Sulfate Reducing Bacteria (SRB) that produce hydrogen sulfide. As a result, gaseous hydrogen sulfide (H2 S) production is eliminated. The treatment requires an initial conditioning period when the biofilm that harbors the SRB’s is removed, followed by maintenance treatments that are repeated as monitored lines show signs of SRB reformation.

The Cloevis technology, delivered as a turn-key, fixed-cost, full-service program, provides the following benefits relative to conventional sulfide control treatments:

  • Avoidance or minimization of onsite chemical storage
  • Independence from sulfide loading, retention time or oxygen uptake
  • No labor/maintenance requirement
  • Removal of sulfide odors for up to three weeks after treatment cycle
  • Elimination of methane production within the treated segment
  • No downstream adverse impacts due to residual treatment chemicals
  • Effective cost similar to caustic shocking and less than nitrate or iron salts
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Sulfide Control with Cloevis Biofilm Removal Service

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Project Scope

A major city in Florida had been experiencing chronic hydrogen sulfide (H2S) odor and corrosion problems at a forcemain discharge manhole and further downstream at a lift station, resulting in community complaints and collection system corrosion. Furthermore, the forcemain was located in the median of a busy roadway with no place to store a permanent chemical injection system. USP Technologies (USP) performed a system trial utilizing Cloevis Biofilm Removal Service. The trial quickly reduced H2S to desired levels at both control points and eliminated all odor complaints.

Technology

Cloevis Biofilm Removal Service (Cloevis BRS) is an innovative technology offering that removes the biofilms that adhere to the inner surfaces of wastewater forcemain walls, including the underlying Sulfate Reducing Bacteria (SRB) that produce hydrogen sulfide. As a result, gaseous hydrogen sulfide (H2S) production is eliminated. The treatment requires an initial conditioning period when the biofilm that harbors the SRB’s is removed, followed by maintenance treatments that are repeated as monitored lines show signs of SRB reformation.

Control of H2S has been achieved in wastewater collection systems with the utilization of many different technologies such as oxidation, precipitation, pH adjustments and vapor-phase systems. Cloevis BRS offers the benefits of lower cost, avoidance or minimization of on-site chemical storage, is unaffected by sulfide loading, retention time or oxygen uptake and has no labor/ maintenance demand. Other benefits include complete removal of sulfide odors for up to three weeks after treatment cycle and elimination of methane production within the treated segment as well as no downstream adverse impacts due to residual treatment chemicals. In addition, the effective cost of Cloevis BRS is similar to caustic shocking and less than conventional continuous chemical feed alternatives such as nitrate and iron salts.

Solution

The City’s forcemain length is 8,600 feet with a diameter of 8-10 inches and a retention time of 4-6 hours. It has a wastewater flow of 0.128 MGD, and prior to Cloevis BRS treatment, had baseline H2S vapor levels at 50-119 ppm and total liquid sulfide levels at 7.8 mg/L at the control location.

The initial conditioning period involved two separate 24-hour treatments which were completed two days apart. Maintenance treatments included one 12-hour treatment after the first 12 days and one 8-hour treatment after an additional 24 days. Ongoing maintenance Cloevis BRS treatments are completed every 3-4 weeks, depending on the rate of biofilm regeneration. Since the initial conditioning period, H2S average levels have steadily been at 5 PPM or less at the forcemain discharge manhole and sulfides at the downstream lift station have been greatly reduced. Additionally, odor complaints have ceased at these locations since USP began Cloevis BRS treatment.

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

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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 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 sludge 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 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 at Holding Tank and Belt Filter Presses via Hydrogen Peroxide

Project Scope

A Midwest wastewater treatment plant was struggling with problematic hydrogen sulfide (H2S) levels at two points within their facility arising from biosolids processing. The factors driving the need for H2S control included worker safety, corrosion of electronics and concrete, implied regulatory limits and odor control. Along with normal residential and commercial flows, the facility also receives unpredictable slugs of high biological oxygen demand (BOD) wastewater from agricultural industries and handles septage hauler loads from a wide radius. USP Technologies (USP) implemented a full-service hydrogen peroxide (H2O2) solution with operator-adjustable dosing options to account for the unpredictable sulfide loadings and to lower H2S to acceptable levels at both their biosolids holding tank and dewatering building.

Technology

H2O2 is ideally suited to remove H2S from wastewater solids, provided that sufficient contact times are available – typically 2-5 minutes prior to the dewatering device. The efficiency of treatment depends upon the available reaction time, the initial level of H2S and the relevance of non-H2S odors. Under optimal conditions, effective dose ratios are about 5 parts H2O2 per part aqueous sulfide, and can be reliably estimated through beaker tests. The chemical reaction is as follows:

H2S + H2O2 S0 + 2H2O

Background

A biosolids holding tank receives all biosolids awaiting dewatering at the plant’s two belt filter presses. The tank is generally emptied every one to three days depending on biosolids generation rates correlated with industrial discharge volumes. The biosolids entering the tank, especially from the gravity thickeners, contain a significant sulfide load throughout the entire year. The holding tank employs mechanical mixing and aeration to minimize further sulfide generation, however, this causes extreme volatilization of H2S, exceeding 500 ppm. Previous control methods, including iron salt addition and “in-situ scrubbing” using a hydroxyl ion generating system only provided limited success in achieving desired targets.

Compounding the challenge, the radicals generated interfered with the proper measurement of H2S. From the holding tank, biosolids are pumped to a dewatering building housing two belt filter presses. The turbulence of these belt filter presses causes most of the sulfide present to volatilize. A wet scrubber was installed and used for years to control the H2S, however, by 2014 it was at the end of its serviceable lifespan.

Solution

USP was invited to visit the facility to determine a more effective treatment strategy. Bench scale dose response tests utilizing shake tests were then conducted to determine theoretical hydrogen peroxide dosing needs and possible reaction times from several injection points. The optimal injection point was determined to be at the biosolids pump outlet, which provided approximately 3 minutes of reaction time before reaching the belt filter presses.

Shortly afterwards, a full-scale H2O2 storage and dosing equipment system was installed. The H2O2 pumps were connected by relays to the biosolids pumps to ensure that H2O2 only dosed while the biosolids pumps were running. The program was demonstrated to be effective within the first hour of operation, with H2S levels brought down below 1 PPM both above the belt filter presses and within the dewatering building’s main room. The program continued with dosing rates throughout the first six months ranging from 1.5 to 6 gallons/hour.

In addition, the operators were trained on how to both raise and lower dosing rates based on the observed H2S levels to mitigate variable industrial loadings. The removal of H2S from the dewatering facility eliminated the need for a costly replacement of their wet scrubber, and the customer invited USP to co-present our success story at their state conference.

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Biosolids Odor Control via Sodium Chlorite and Calcium Nitrate

Project Scope

In upstate New York, a wastewater treatment facility historically utilized potassium permanganate to control odors at two locations in their biosolids processing operations. The first location was into the waste activated sludge (WAS) fed to a gravity belt thickener. The second location was into a mixed stream of primary sludge and thickened WAS blended in holding tanks and pressed before incinerating. In October 2014, the plant’s incinerator went down. Pressed solids were hauled off-site for disposal in a landfill. The plant began to receive odor complaints from the truck drivers and the landfill personnel, so the treatment rate of permanganate was doubled. This attempt at durational odor control was unsuccessful and the cost was $480,000 per year. The plant had been using a nitrate product for durational odor control in its collections system and learned from a nearby plant about USP Technologies’ successful application of a sodium chlorite based oxidant blend (chlorite) for immediate odor control supplemented with a nitrate solution (nitrate) for durational odor control. USP Technologies (USP) was then brought in to trial a similar solution.

Technology

Chlorite oxidizes hydrogen sulfide and organic odors without producing any harmful by-products such as chlorinated organics. Chlorite is very fast reacting, on the order of seconds, with hydrogen sulfide and organic odor compounds. As a result, it can be added directly to the sludge in the feed lines prior to the presses. The chemical reaction at neutral-acid pH:

2 H2S + NaClO2 → 2 S<>0 + HCl + NaOH + H2O

and at alkaline pH:

S<>2- + 2 NaClO2 → SO<>42- + 2 NaCl

Neutral-acidic conditions are favorable, as it only requires 3 mg/L sodium chlorite per 1 mg/L sulfide.

Like permanganate, chlorite is not as effective at durational odor control, so nitrate was selected to perform this role. Sulfate reducing bacteria, under anaerobic conditions (as is the case in sludge holding tanks), typically use sulfate as a source for oxygen. When nitrate is present, however, the bacteria will preferentially select nitrate as its source of oxygen, preventing the sulfate from being reduced to sulfide and subsequently preventing the formation of hydrogen sulfide gas. Also, with an alternative oxygen source, other common bacteria can now consume dissolved sulfide ions and oxidize them back to sulfate and/or elemental sulfur, further reducing sulfide available to form hydrogen sulfide gas.

Solution

USP replaced the two potassium permanganate dosing locations with chlorite, and a separate nitrate dosing location was installed at the presses. Three 1,000 gallon tanks were installed for chlorite as well as a 14 gph diaphragm chemical metering pump at each dose point, which was interlocked into the plant’s SCADA system. At the gravity belt thickeners, the H2S levels were typically low but there are other problematic organic odors which are effectively oxidized with chlorite. At the belt filter press, H2S gas levels were higher (35-55 ppm) since the primary and waste activated sludges fed to the press typically sit in holding tanks for anywhere from a day to two weeks. The plant has ventilation hoods above each press that bring the gas to a scrubber, but the odors in the room were still strong enough to cause discomfort to the operators in the vicinity.

An H2S monitor was hung at the press for continuous monitoring of H2S. Once the chlorite feed system was installed, sulfide in the sludge was able to be effectively oxidized, reducing the H2S gas at the press from 35-55 ppm down to 0-3 ppm. Figure 1 shows the effect of the chemical program. Additionally, as the data towards the right hand side of the graph depicts a point in time when the chemical feed was lost (a valve was closed).

When not incinerated, the dewatered solids are hauled off-site for disposal at a landfill. The potassium permanganate provided very little, if any, odor control once the solids were loaded into the trucks, leading to many odor complaints. The addition of nitrate at the belt filter press via a 2,500 gal storage tank and dosing system proved

to be effective as it completely eliminated further odor complaints. It is the plant’s plan to stop using their incinerator in March 2016, at which point nitrate will be used continuously.

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