Journal of Environmental Engineering

Ground‐water quality and ground‐water usage in the United States, laws and policies currently in force that affect ground‐water quality protection and restoration of contaminated ground waters, current technologies for pollution prevention and aquifer restoration after contamination, research activities and needs to deal with present and future ground‐water protection, and restoration efforts are discussed. It is concluded that present U.S. federal laws are more than adequate to protect and clean up the nation's ground waters; compliance with existing ground‐water pollution prevention legislation will be most effective. While national interest in the protection and cleanup of the nation's ground waters is well justified, panic over the current status of ground‐water quality is not. Research needs to be expanded on how to prevent substances from being released to the environment during handling, treatment, storage, or disposal, with specific emphasis, on loss control, along with continued efforts to develop and refine methodologies to clean up contaminated soils and aquifers.

Shrinkage can effect significant consolidation of saturated filter cakes, and results in production of filtrate that must be omitted from specific resistance calculations. Shrinkage results when curved air/liquid interfaces bounded by solids form at filter cake surfaces following the cake formation stage. The resultant decrease in porewater pressure is described by the Young‐Laplace equation, which was used to express mathematically the effective stress causing shrinkage. In situ porewater pressure measurements corroborated the onset of shrinkage of a kaolin filter cake. Synchrotron x‐rays were used to monitor temporal and spatial cake suspended solids concentration changes, and significant shrinkage of an activated sludge filter cake was observed. Cake‐suspended solids concentration data were combined with filtrate production data to obtain singular values of the cake‐suspended solids mass deposited per unit volume of filtrate produced by a kaolin slurry and an activated sludge. Values of this parameter were determined by two other means to illustrate how errors in specific resistance calculations can result when the onset of shrinkage is not ascertained.

The ability of immobilized cells grown under oxic and fluidized conditions to degrade 4‐chlorophenol (4‐CP) and 2,4‐dichlorophenol (2,4‐DCP) is evaluated under different dilute rate conditions. Microcarriers with 6.5‐μ. pores are employed for cell immobilization and retention. Results indicate that, with feed 4‐CP and 2,4‐DCP concentrations at 35.7 and 45.3 mg/1, respectively, good and stable removal performance is achievable at empty‐bed hydraulic retention times as low as one hour. Stoichiometric release of chloride and removal of total organic carbon are also observed, implying that complete mineralization of 4‐CP and 2,4‐DCP is attainable. This observation is further validated with the gas‐chromatography/mass‐spectrometry (GC/MS) data obtained in the 2,4‐DCP experimentation. Colonization of immobilized cells on the microcarrier surface is a slow but selective process. Extensive growth of filamentous bacteria is observed, with rodshaped bacteria grown underneath and adhered to the filaments. Detachment of immobilized cells from the microcarrier surface is negligible. The formation of microbial films on the microcarrier surface with measurable thickness is absent.

The effects of ammonia on mesophilic digestion of acetate, propionate, acetate‐propionate mixture, and lactate were studied in batch serum bottles. The un‐ionized ammonia nitrogen (UAN) affected the acetate‐utilizing microorganisms in the acclimated mixed cultures to a greater extent than propionate‐utilizing bacteria or other trophic groups. The inhibitory effects were less severe in batch reactors supplemented with sulfate, pointing to an antagonistic action of the sulfate‐reducing bacteria. Analysis of the inhibition pattern of methane/biogas production has shown that UAN displayed a moderate half‐kill dose in the range of 10 millimole and demonstrated a high sensitivity exponent. The latter suggests potential for a sudden failure response of an anaerobic system subjected to an increasing ammonia concentration in the reactor.

Septic tank effluent (STE) is applied to stratified sand filter columns at a rate of 6.1 cm/day (1.5 gal/day/sq ft) and the ability of the sand filter to remove enteric viruses is demonstrated. The sites of virus retention are determined. Seven 10‐cm (4‐in.) diameter sand columns are constructed of 25 cm (10 in.) of dry, coarse sand, 10 cm (4 in.) of dry, fine sand, and 25 cm (10 in.) of glass sand, with the sand layers separated by 5 cm (2 in.) of 1.9‐cm (3/8‐in.) rounded gravel. Household septic tank effluent containing poliovirus vaccine (Type I, strain LSc) is applied to the filters, and influent and effluent samples are collected. Enterovirus analyses are performed using plaque assays in buffalo green monkey (BGM) kidney cell cultures. Following the filter runs, the columns are dissected into 2.5‐cm (1‐in.) discs and the discs were assayed for enteroviruses. The filter columns retain all viruses when the virus loading remains less than 33,000,000 PFU/1 (plaque‐forming units per liter). Analyses of the filter discs show most viruses are retained in the top few centimeters of biologically active sand, and a mass balance reveals virus inactivation in the sand filter.

Sewage air at the inlet works of a municipal wastewater treatment plant, was simultaneously pumped through two pilot columns, one filled with an alkali‐impregnated carbon material, while the other was filled with a nonalkali‐impregnated grade. Odor and $H_{2}S$ concentrations at the influent and effluent ports of the carbon columns were continuously monitored for about eight months. The odor and $H_{2}S$ concentrations of the influent sewage air varied significantly throughout the study period, averaging $120\mathrm{SOU}/m^3$ and 5.3 ppm, respectively. Breakthrough of odor at the effluent ports occurred earlier than that for $H_{2}S\text{,}$ and the initial breakthrough odor was exerted mainly by non‐$H_{2}S$ compounds. Although the alkali‐impregnated carbon was capable of removing a much larger quantity of $H_{2}S$ than the nonalkali‐impregnated grade, its effectiveness in removing other odorous but non‐$H_{2}S$ gaseous compounds was less significant. The cost of using nonalkali‐impregnated activated carbon for odor removal was comparable to that of the alkali‐impregnated carbon. This cost comparison, however, ignores the effect of regeneration of the carbons.

The effects of varying the height and number of stages and feed rate for nonpulsing, passive‐pulsing, and active‐pulsing air classifiers is studied for the separation of complicated particle mixtures. All of the air classifier configurations tested achieve high $(>94\%)$ maximum separation efficiency. Increasing height is found to increase the range of air flow over which separation efficiencies greater than 90% are achieved. Decreasing feed rate has a similar effect. For each of the three classifiers studied—nonpulsing, passive pulsing, and active pulsing—the tallest classifiers at the lowest feed rates achieved the broadest efficient separation range. Results indicate that the passive‐pulsing air classifier performs better than the active‐pulsing air classifier, which in turn performs better than the nonpulsing air classifier.

The conventional windrow and aerated windrow processes are viable sludge‐disposal options that produce marketable end products. Both methods entail constructing long parallel rows containing a mixture of sludge cake and amendment and turning the rows frequently with mobile equipment. The conventional process relies on natural ventilation whereas the aerated method uses forced mechanical aeration in addition to natural ventilation. Major drawbacks of the conventional process include excess odor generation and susceptibility to upset from adverse weather. Odor control is a major advantage of aerated windrow composting; these systems, however, are more capital intensive than the simpler conventional systems. The Sanitation Districts of Los Angeles County, California, operate a state‐of‐the‐art conventional windrow facility at the Joint Water Pollution Control Plant in Carson, California. The operation uses two composting steps and two different composting machines. Quality‐control monitoring has shown that the two‐step method provides excellent disinfection and produces a dry product during most of the year. Rainy weather and cool air temperature reduce the drying rate, resulting in the production of a wetter compost during the winter.

A method is presented for estimating vertical mixing coefficients in overland flow with rainfall using laboratory data and using a mathematical model of shear‐flow convection, rainfall dilution, and vertical mixing. The laboratory data consist of concentration‐time measurements downstream from an injection of a conservative dye into overland flow during rainfall over a smooth impervious surface with constant slope, without sediment and with flow in the laminar Reynolds number range. Results of the mathematical model are compared to the concentration time measurements to calibrate values of the vertical mixing coefficient. The calibrated values of the vertical mixing coefficient were most highly correlated to slope and a Reynolds number related to rainfall intensity. An analysis of the calibrated vertical mixing coefficient values using equations for eddy turbulence did not prove satisfactory.