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Contract operation, maintenance and management (OM&M) of a municipal water treatment plant are fairly straightforward concepts. For a fixed fee, the private OM&M firm operates the plant according to regulatory requirements and supplies a prescribed volume of drinking water to the municipality. OM&M contracts may be detailed and lengthy, but the essentials remain the same-service and compliance for a reasonable price.
While it might be a simple concept, unforeseen issues can influence cost and compliance. These problems can be related to correcting a pre-existing problem (often the motivation for a municipality to contract with a private operator) or anticipating new and increasingly strict environmental regulations that could have a significant impact on a plant's compliance record. This was the case at Newark, N.J.'s Pequannock Water Treatment Plant located in West Milford, N.J. A pilot study of an alternative water treatment process was conducted earlier this year in response to proposed disinfection by-product rules.
The potential for compliance difficulties exists because of additional rules for disinfection and disinfection by-products (D/DBP) now being proposed by the Environmental Protection Agency (EPA). The new rules would require the level of trihalomethanes (THMs), a by-product of chlorination, be reduced in the city's drinking water. The City of Newark is currently meeting the disinfection by-product maximum contaminant level (MCL) of 100 parts per billion (ppb) for THM, but the EPA is proposing to reduce the MCLs for THMs to 80 ppb. Additionally, haloacetic acids (HAA) are expected to be included in the new D/DBP rules. The MCLs for HAAs are anticipated to be 60 ppb.
The city and its private OM&M firm have been working together to ensure that the plant complies with the proposed EPA regulations. The Newark treatment plant cannot simply lower the amount of chlorine used in disinfection to reduce the level of THMs. This would increase the risk of inadequate disinfection and could increase the presence of cryptosporidium and giardia in the city's drinking water.
An EPA Information Collection Rule (ICR) requires cities larger than 100,000 people to monitor for cryptosporidium. Of the 300 cities affected by the ICR, the National Association of People with AIDS has singled out six metropolitan areas, including Newark, as being locations of special concern. People with weakened immune systems are particularly at risk for the presence of cryptosporidium.
Ozone is an extremely strong oxidizing agent. In fact, ozone is so reactive to various water contaminants that it generally does not survive very long in the treatment process. Ozone reacts with natural organics in the water supply and forms lower molecular weight organic by-products that tend to be biodegradable.
Ozone has been used in water treatment systems for more than 90 years, mostly in Europe and especially in France. An increasing number of water treatment systems in the United States are utilizing ozone for disinfection due to the increase in regulatory requirements. Ozone installations in the United States have increased from less than ten in 1980 to more than 100 in 1994, with the majority of new plants using the technology having capacities more than ten MGD.
The private firm was responsible for overseeing the design, installation and operation of the pilot ozonation system at no cost to the city for personnel or equipment. Through its corporate affiliates company, Compagnie Generale des Eaux, Praxair-Trailigaz and Metcalf & Eddy, Inc., PSG had access to advanced technologies and the engineering expertise necessary to install and test the customized pilot system. INUSA Instruments supplied the necessary instrumentation to measure the ozone and the ozone residual during the pilot study. PSG conducted the microbiological analyses and the City of Newark provided the organic analyses through a private laboratory. The study was initiated to determine the most effective dosage, contact time, D/DBP effects and general microbiological effectiveness associated with ozonation. The study was conducted over a three-month period in early 1997.
The ozonation system was assembled in the plant's pretreatment screen building, where a raw water supply was readily available. This system was designed to be simple and functional, while also being easy to dismantle at the end of testing. The pilot plant consisted of a 20-foot, six-inch clear PVC column with a diffuser located at the bottom of the column. Raw water flowed into the column from the top to the bottom, with sample taps located at various places along the column. The instrumentation consisted of a raw water flow meter, ozone generator, ozone feed gas analyzer, ozone analyzer, oxygen generator, high-quality air compressor and related piping. The support structure for the flow meter, contact column and instrumentation was mounted on two, 4¢ x 8¢ sheets of 3¦4-inch thick plywood. The other related generating units were floor mounted. Ozone destruction units were installed on all discharge points on the column and the instrumentation.
The ozone generator used in the study utilized a dry oxygen feed for the production of ozone. The oxygen feed unit is a separate system that consists of an air compressor and the oxygen generator that supplies the oxygen to the ozone generator. Oxygen is introduced at this juncture to the ozonator and distributed in a set of stainless steel cells containing the dielectric tubes where the oxygen-to-ozone conversion is conducted.
The microbiological testing protocol was the Heterotrophic Plate Counts (HPC) that were run on tryptone glucose yeast agar and incubated at 35° C for 48 hours. The coliform analyses were done on the membrane filter method using m-Endo broth and incubated for 24 hours. These analyses were conducted at each dosage level. Testing for HAAs, Total Trihalomethanes (TTHM), Total Trihalomethane Potential (TTHMP) and Total Organic Carbon (TOC) was also conducted at each dosage level. The same analyses were also conducted on chlorinated raw and on the distribution water.
Each run was completed in a day and the samples were submitted for analyses the same day. Three runs were performed each month during the three-month study. Analyses were run on raw water, chlorinated raw water and the plant's distribution water. A raw ozonated/chlorinated sample also was run to determine the effect of chlorine on an ozonated sample. The raw ozonated sample received approximately the same dosage of chlorine (1.0 ppm) that was applied to the distribution water with a contact time of 60 minutes. This gave a free-chlorine residual level of 0.8 to 0.9 ppm to the test samples. No filtration was conducted on the ozonated samples prior to the chlorine addition.
Analytical data developed from the three runs clearly indicated THMs and the HAAs could be reduced and could meet the proposed and current disinfection by-product rules. The ozonated sample that was chlorinated also met proposed MCL levels for THMs and HAAs. No significant levels of bromates (BrO4) were found. The study also found TTHMP levels were not great in the ozonated and ozonated/chlorinated samples.
The microbiological data indicated that ozone is as effective as chlorine for disinfection. Both the HPCs and the coliform analyses indicated acceptable disinfection. In all cases, the ozonated samples at all dosages and contact times were negative for coliform.
This study conducted by the private firm and the city indicates ozonation to be a superior microbiological disinfection system, resulting in the reduction of other DBPs. Other studies have indicated no major health risk by-products are produced by using ozonation as a disinfectant.
In the best sense, a municipality and its private OM&M operator are partners with a true mutuality of interest. If a water plant is out of compliance, neither party's interests are served. Working together, the City of Newark and the private OM&M firm anticipated potential compliance problems rather than responding to them after the fact.