Preliminary and primary wastewater treatment steps are important for the entire wastewater treatment process. They set the stage for all subsequent treatment steps, ensuring a plant runs smoothly and equipment functions at maximum efficiency so the final effluent is as clean as possible. If preliminary and primary treatment are not done, solids, fibrous materials and grease can clog and damage pumps, overload secondary systems, or cause costly maintenance and equipment replacement problems.
Preliminary Treatment
The goal of preliminary and primary treatment is to remove grit, solids and other large objects that inevitably form part of the wastewater treatment plant’s raw wastewater. Preliminary and primary wastewater treatment is one of the most labor-intensive parts of a plant operator’s job. It can introduce several operational surprises and occupy a considerable amount of time. It also can introduce expensive capital and maintenance costs.
Plants often employ too many steps in the early stages of treatment, requiring more work than necessary. For example, raw wastewater enters grit chambers so inorganic solids can settle out. Then wastewater is pushed through either coarse or fine screens and flows to a clarifier or a dissolved air flotation system for suspended solids removal.
At this stage, wastewater can be sent to secondary treatment to digest biodegradable organic matter and remove excess nutrients. Depending on post-treatment intentions, wastewater may also need to be treated to advanced tertiary standards.
Initial wastewater treatment steps can be simplified with the proper technology. The ADI-BVF reactor is a biological treatment technology that requires no upfront suspended solids or fats, oils and grease (FOG) removal.
The reactor can digest organic solids and FOG that normally would be removed by physical treatment. Basic coarse screening and potential grit removal typically are all that is required before wastewater is introduced. The reactor can treat wastewater streams with moderate to high concentrations of organics, suspended solids and FOG. This anaerobic digestion system combines primary and secondary treatment. The system is sized to work at low volumetric loading rate conditions, and designed to handle variations in wastewater flows and characteristics. The low-rate nature of the reactor maximizes biogas production, so plants have more opportunity for green energy recovery.
The small number of moving parts within the reactor results in low maintenance requirements and operator attention. The system also offers the ability to store waste sludge, allowing for flexible sludge wasting.
Examples of Simplified Treatment
The Milton Regional Sewer Authority (MRSA) in Northumberland County, Pa., treats municipal and industrial wastewater. Consumer demand caused a nearby food manufacturing plant to increase production, which led to organic overload in the aeration tanks at MRSA’s wastewater treatment plant, even after primary treatment. In addition to the increase in flow, the wastewater strength was expected to increase by up to 30%.
MRSA required a cost-effective wastewater treatment solution to meet effluent limitations and combat high sludge disposal charges and energy costs. MRSA piloted a wastewater treatment system using BVF technology.
ADI Systems designed and installed two full-scale 7.5-million-gal BVF reactors at the wastewater treatment facility. The reactors remove approximately 90% of the organic load from the wastewater with no primary treatment. The reactors also can receive septage and other hauled-in wastes.
This resulted in savings in labor costs and energy bills. Compared to aerobic wastewater treatment, the low-rate reactors produce approximately 90% less sludge. This, in combination with biosolids drying, has lowered sludge disposal costs and saved valuable landfill space.
Biogas collected in the reactors is burned in two 1,000-kW gas engines to generate electricity, helping power the treatment process and eliminate hundreds of thousands of dollars in annual electricity costs. Excess electricity is sold to the local utility. MRSA has also reduced its reliance on fossil fuels and carbon dioxide emissions.
The city of Tulare, Calif., is located in the San Joaquin Valley, which has some of the strictest environmental regulations in the nation. Noncompliance can be costly—up to $10,000 a day. Tulare’s wastewater treatment plant handles large volumes of both domestic and industrial wastewater.
Tulare originally used large aerated lagoons to aerobically treat wastewater, but as flow increased and discharge regulations became stricter, the city council decided to expand and upgrade the facility. It wanted an efficient, low-maintenance method of treating wastewater that would meet the demands of California’s environmentally sensitive water control laws and did not involve chemical addition or expensive and labor-intensive processes.
The BVF reactor was selected to pretreat Tulare’s wastewater. It treats 2 to 4.4 million gal per day. This technology helps the city comply with environmental discharge limits and recover green energy potential. A 31-million-gal lined basin converts organic matter in the wastewater into biogas as part of the anaerobic treatment process.
The biogas produced from this waste-to-energy solution allows the city to be more self-sustaining and reduce the environmental impacts of electricity use. It provides heat for the digester and supplies the city with green energy that minimizes energy consumption.
