Characterization, utilization and treatment of mechanized clam processing wastes

In response to water quality deterioration caused by clam processing effluent, the Virginia State Water Control Board is imposing much greater effluent discharge limitations on the industry. Meeting these limits will require increased wastewater treatment and decreasing the water volume of water used and the loading of organic material and suspended solids. Disposal of sludges and solid wastes also present problems to the industry. Three processing plants were studied to characterize the nature, sources and variations in waste generation and to evaluate potential solutions.

Wastewater is generated throughout the processing plants from washing operations, from splashing and overflow of tanks and flumes and from cleanup operations. Wastewater generation varied from plant to plant and at each plant over time, ranging from 80,000 gallons to almost 350,000 gallons per day and as high as 40,000 gallons per hour. The organic loading in wastewater ranged as high as 15,000 mg/L COD and averaged 3000-7000 mg/L. Total suspended solids loading ranged as high as 29,000, and were usually between 1,000 and 10,000 mg/L.

Anaerobic digestion and composting of solid wastes were evaluated by bench scale experiments. Anaerobic digestion can provide reduction in COD of 75% and generate usable biogas. Composting can be used to stabilize sludges and solid wastes with destruction of the organic fraction in seven days.

The proposed 90 mg/L BOD and 90 mg/L TSS limitations are not significantly stricter than the limitations imposed on similar plants in other areas.