Retention Of Suspended Solids Research Articles

The Use of Biofiltration for Further Wastewater Treatment

The City of Mannheim (FRG) expanded its one stage biological treatment plant by addition of a second stage based on dry bed filtration and designed for an average wastewater flow of QTW = 8.800 m3/h and an average BOD5 of 70 mg/l. Five firms in the foreground of process selection conducted from 1980 to 1982 experiments on purification systems for the effluent from the first biological stage. Systems tested were biofiltration in dry and submerged beds and activated two sludge systems. Filter materials used were inert material, activated carbon and Biolite. In one case a pretreatment by coagulation was employed. The influent of submerged filters without coagulation was supplied with technical oxygen whereas submerged filters with coagulation were supplied with atmospheric oxygen. The two sludge process employed a plastic medium (Flocor E) in an aeration tank of up to 40% total bed volume; aeration was achieved with compressed air. The results of the submerged filtration tests are compared to those of the two sludge system with respect to retention of suspended solids, elimination of BOD5 and COD and soluble and total nitrogenous compounds. A procedural evaluation and cost comparison are made. In addition the problems that arise by solution of oxygen up to high concentrations are indicated and solution possibilities discussed.

Dredged Material Sedimentation Basin Design

Procedures have been developed for designing dredged material sedimentation basins. These procedures can also be used for designing sedimentation basins for other slurries having high suspended solids concentrations. Dredged material sedimentation basins are slightly different from those used in water and wastewater treatment in that the dredged material basins must provide for sedimentation to achieve acceptable ef0uent quality while providing storage volume for several years of material dredged from local waterways. Guidance is presented for field sampling and laboratory testing required to obtain data for sediment characterization, data analysis, sedimentation basin (containment area) design, and estimating storage capacity required. Settling tests performed in a 8‐in. (20 cm) diam column were found to be satisfactory for defining dredged material settling behavior. Settling behavior in the freshwater environment was best described by a flocculent settling test, while behavior in a salt‐water environment was best described by a zone settling test. Procedures are presented for designing new containment areas for suspended solids retention and for evaluating the suspended solids retention potential of existing containment areas during planned disposal activities. The field verification work performed during this research indicated that conservative values could be estimated from laboratory tests for solids concentrations expected in the dredged material sedimentation basins.

Containment area sizing for disposal of dredged material

Procedures are given for containment area sizing for retention of suspended solids based on the settling characteristics of the dredged material. Separate sizing procedures for freshwater and saltwater sediments provide for determination of the respective surface area or detention time required to accomodate continuous dredged material disposal. Procedures are given for the laboratory testing required to obtain data for sediment characterization, containment area sizing, and estimates of storage capacity required. These procedures can also be used for designing containment areas for other slurries having high suspended solids concentrations. Settling tests performed in a 20-cm-diam column were found to be satisfactory for defining dredged material settling behavior. Settling behavior in the freshwater environment was best described by a flocculent settling test, while behavior in a saltwater environment was best described by a zone settling test. The same settling columns were used for both tests withonly minor procedural changes. Procedures are presented for designing new containment areas for suspended solids retention and for evaluating the suspended solids retention potential of existing containment areas during planned disposal activities.

Contaminant mobility in diked containment areas

Nine dredged material land containment areas, located at upland, lowland, and island sites, were monitored during hydraulic dredging operations in fresh and brackish-water riverine, lake, and estuarine environments. Influent/effluent sampling at the diked disposal areas showed that, with proper retention of suspended solids, most chemical constituents could be removed to near background water levels. Most heavy metals, oil and grease, chlorinated pesticides, and PCBs were almost totally associated with solids in both the influent and effluent samples. The parameters that appear to have the greatest potential impact as a result of land disposal of dredged material are ammonia, soluble manganese, total mercury, and dissolved oxygen; soluble iron, zinc, and copper may occasionally exceed criteria or background levels.v However, none of these should present serious problems after dillution of the effluent discharge in the receiving waters. Actively growing vegetation in disposal areas appeared to be efficient in removing ammonium nitrogen to low levels and also for filtering out suspended solids. Dissolved oxygen in effluents ranged from 0.6 to 12.5 ppm. Geochemical phase partitioning of influent and effluent solids indicated that carbonate solids of several heavy metals tended to form during dredged slurry containment, promoted by high alkalinity and increased pH in site waters. Metal adsorption onto effluent suspended particles (exchangeable phase) increased slightly, along with a significant increase in cation exchange capacity.

Nutrient and Sediment Retention in a Temperate Marsh Ecosystem

AbstractThe Wye marsh, an undeveloped wetland of 639.9 ha, serves as a receiving water for a 19,600 ha agricultural watershed before discharging into the Great Lakes. Seasonal and diel changes in limnological variables, most notably nitrogen, phosphorus, silica and turbidity, have been examined in the Wye river, marsh and discharge waters over an 11‐month period and related to the composition of marsh sediments. Retention rates of the marsh ecosystem for incoming nutrients and suspended solids have been estimated by calculations of mean monthly inflow to outflow ratios using the levels of these factors in the Wye River and the marsh discharge. Calculated mean monthly retention rates of the marsh for incoming nutrients is estimated at no less than 61% for nitrogen‐N, 36% for total phosphate, and 14% for soluble silica during the ice‐free period. Based on observed turbidity levels, the retention of incoming suspended solids is estimated at 65% for the same period. The Wye marsh is a substantial sump for inorganic and organic materials which are retained within the water column, biomass and unconsolidated sediments.