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Within a 100-mile radius of the City of Houston there are over 700 municipal wastewater treatment plants. A regional approach is used to manage the biosolids from the wide variety of types and sizes of facilities in the area. During the winter in Houston the weather pattern often produces rain every 5 or 6 days with little soil drying between rain events. During this period land application of liquid biosolids cannot meet the regulation prohibiting the application of biosolids to saturated soils.

The predominate type of wastewater treatment plant has a flow of under 1,000,000 gallons per day, utilizes aerobic digestion with fill and draw thickening sludge processing, and produces liquid sludge with a solids concentration of 2.5 to 3.5 %. Few of the facilities have storage capabilities. Additionally some treatment plants dewater their biosolids using belt presses.

A regional approach to biosolids management has been developed. A private company provides management to over 40% of the facilities. To remain compliant during wet weather and provide the timely removal of biosolids, an alliance with a Municipal Utility District to use an underutilized wastewater treatment plant was formed. The District provided power and treatment of filtrate through the existing wastewater treatment plant. The private company constructed a regional biosolids processing facility.

By utilizing its unused capacity the utility district has improved its financial condition and continued to provide relatively low water and sewer rates to its other customers.

The facility includes blending of sludges, dewatering with belt presses, and if necessary lime stabilization. Lime stabilization is not presently required. Generating facilities that send their biosolids to the processing facility must continue to provide PCB, TCLP, and land application metals testing to contribute their sludge. Nutrients, pathogen, and vector control testing are not required. By only accepting sludge that is non-hazardous and meeting the metals requirements for land application the integrity of the program is ensured. Over 5,000,000 gallons of liquid sludge is accepted at the processing facility every month.

Biosolids taken from the regional sludge processing facility are tested at a more frequent interval than the regulations require. The data has consistently shown that biosolids leaving the facility meet all EPA and Texas requirements for land application.

Biosolids are beneficially land applied unless prolonged wet weather closes the farms. When the farms are unable to be used the biosolids are landfilled in private co-disposal landfills.

The private company also provides transportation and land application of cake biosolids from facilities that dewater their sludge. For larger wastewater treatment plants that do not have in-house dewatering capabilities the private company provides mobile dewatering, transportation and disposal.

The regional approach continues at the farm. Each beneficial land application farm is registered with the State of Texas to accept biosolids from multiple facilities. A computer program was developed to track the nutrient and metal loadings from all of the participating generators.

This regional approach allows environmentally sound, economically viable sludge management for small wastewater treatment plants. The approach allows the compliant operations year round.

Other benefits of this program include fewer trucks on roads leading to the farms compared to the direct land application of liquid biosolids. The practice of spreading cake biosolids with manure spreaders is more accepted by the farmers and surrounding public than spray irrigation or trucks spreading on the land. Short-term staging of cake biosolids has less environmental impact than spreading liquid biosolids on wet or saturated soils. Overall this program reduces the complaints by the regulatory agency or the general public.

Document Type: Research Article


Publication date: 2002-01-01

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