Electrolytic treatment of an industrial wastewater from a hosiery plant.

Textile plant wastewater being treated in a facultative pond system had too high of a solids concentration to be reused in the dying and rinsing processes. Electrocoagulation was evaluated to further treat the pond effluent to remove turbidity, which was caused by dyes and microorganisms. A range of amperages were tested for removal of turbidity and chemical oxygen demand (COD). Electrocoagulation lowered the turbidity from 1400 NTU to below 50 NTU; and COD was lowered from 550 mg/L to approximately 250 mg/L, which was acceptable for reuse. In addition, a laboratory-scale sedimentation study was conducted on the electrocoagulated pond effluent, which indicated that a settling time of 35 minutes would provide for 80% removal of suspended solids, which was acceptable for reuse of the water in plant processes.

An evaluation of the urban stormwater pollutant removal efficiency of catch basin inserts.

In a storm sewer system, the catch basin is the interface between surface runoff and the sewer. Responding to the need to improve the quality of stormwater from urban areas and transportation facilities, and spurred by Phase I and II Stormwater Rules from the U.S. Environmental Protection Agency, several companies market catch basin inserts as best management practices for urban water quality management. However, little data have been collected under controlled tests that indicate the pollutant removal efficiency of these inserts when the inflow is near what can be expected to occur in the field. A stormwater simulator was constructed to test inserts under controlled and replicable conditions. The inserts were tested for removal efficiency of total suspended solids (TSS) and total petroleum hydrocarbons (TPH) at an inflow rate of 757 to 814 L/min, with influent pollutant concentrations of 225 mg/L TSS and 30 mg/L TPH. These conditions are similar to stormwater runoff from small commercial sites in the southeastern United States. Results from the tests indicate that at the test flowrate and pollutant concentration, average TSS removal efficiencies ranged from 11 to 42% and, for TPH, the removal efficiency ranged from 10 to 19%.

Factors affecting ballasted flocculation reactions.

Ballasted flocculation represents a relatively new technology that shows promise of bringing improvements to the field of water and wastewater treatment. Ballasted flocculation involves the addition of a ballasting agent (high-density microsand, sp gr = 2.65) to a chemically stabilized and coagulated suspension of particulate solids. Tests were conducted to determine the effect of eight independent parameters on the settling velocity of the resulting floc. Measurements showed settling velocities ranging from approximately 100 m/h for 0.5-mm diameter particles to as high as 380 m/h for particles having effective diameters up to 7 mm. Settling velocities for discrete microsand particles and discrete ballasted flocs were found to fit conventional settling theory with reasonable accuracy. The most important factors contributing to the benefits of ballasted flocculation are the large floc sizes that can be maintained, the greater roundness of the floc particles, and a lower shape factor for the ballasted floc, which all contribute to higher settling rates. Higher settling rates allow for substantially smaller sedimentation units and decreased capital costs.