Search

The dilemma faced by the farm installing an anaerobic digestion system producing more biogas than its energy requirements to maximize the value of the additional gas produced by either converting the excess biogas into electricity for sale to the grid or enhancing the biogas to pipeline-quality renewable natural gas (RNG), are discussed. The analysis of considerations and costs for selling the gas through the electric grid or the natural gas pipeline is presented.

An overview on sewage treatment processes is presented. Methods include peat filters, single-pass sand filters, aerobic treatment units, drip distribution, recirculating media filters and constructed wetlands.

The emerging field of sewage chemical-information mining is taking advantage of a readily available yet underappreciated resource: the untreated waste flowing under our feet and the biosolids remaining after treatment. [...]

A significant potential exists to lower energy consumption and reduce sludge production by incorporating anaerobic processes into wastewater treatment trains. The specific treatment arrangement studied in this case is the anaerobic treatment of primary clarifier effluent of wastewater treatment plants. Anaerobic batch assays showed that the primary clarifier effluent used in this study was ultimately 90% or more anaerobically biodegradable, thus suitable for anaerobic treatment. The anaerobic expanded bed reactor (AEBR) performed well over a wide range of influent CODs and temperatures, especially under severe conditions (5 [degrees] C and 50 mg/L influent COD). The most efficient treatment was obtained with HRTs of three to six hours and influent COD of approximately 150 mg/L. Start-up of the reactor took about 60 days at 30 [degrees] C and 80 days at 20 [degrees] C.

Microbial granulation was examined in four lab-scale upflow anaerobic sludge blanket (UASB) reactors under varied microbial load indices (MLIs). The dimensionless MLI is defined as the ratio of the sludge loading rate to the specific methanogenic activity, and represents the relative substrate sufficiency subjected to by the sludge. A synthetic feed consisting of glucose, peptone, and meat extract was used as substrate and anaerobic digested sludge as seed. The four reactors were designed with the same diameters yet different heights, aiming at achieving a different biological selection pressure (solely MLI) yet a similar physical selection pressure in the reactors. Granulation under the high MLIs of 0.8 and 0.6 developed well within three and four months of operation, respectively, whereas that under the low MLIs of 0.3 and 0.2 did not even after six months. The granulation process was characterized by three phases of acclimation, granulation, and maturation. The MLI provides a quantitative approach toward stepwise sludge loading rate increases during start-up, with the appropriate values of 0.6-0.8 for fast and well-proceeded granulation.

The biodegradation of tributyl phosphate (TBP) by new microbial isolates is coupled to the removal of uranium from aqueous solution in a flow-through system. The proposed products of the degradation are expected to be useful, with the liberated 1-butanol as a biomass growth substrate and the co-released inorganic phosphate moiety as a ligand that can precipitate with heavy metals to retain these as biominerals on the biomass. The approach can be a method for the treatment of TBP-loaded wastes and can be useful for waste phosphotriesters as additives to wastes from metallurgical industries.

The high purity oxygen activated sludge process requires more advanced controls as compared to the conventional activated sludge process. Feedback controllers have difficulty controlling process disturbances due to process delays and noisy signals, and cannot adjust to extreme upsets, such as stormwater flows. Four fuzzy logic control systems were developed for average conditions, and are superior to conventional feedback control systems in conserving energy, reducing dissolved oxygen (DO) variations, and stabilizing feed and exit gas flow rates. A direct control strategy, using feedforward aerator speed control and feedback stage 4 DO control, is the best among the four systems. For plants without variable speed aerators, feedforward control based on influent flow rate to adjust the stage 1 pressure setpoint, with feedback stage 4 DO control, is best. To address stormwater flows an adaptive fuzzy logic control system was developed. The control system can immediately shift to a new state to adapt to large changes in influent flow rate. The system prevents DO depletion under wet weather conditions, and conserves oxygen and energy during dry weather conditions.

Photochemical incineration of anthracene was conducted to investigate proper disposal techniques for toxic and municipal waste. A flowing gas experiment was undertaken, where anthracene vapor was diluted in 1 atm of filtered compressed air and flowed through the all-quartz cell of 50 cm. length and 38 mm. diameter. Results showed the thermal and the photon-assisted thermal destruction of anthracene.

A summary of the 1992 survey results of municipal sewage sludge composting projects is presented. These projects are identified as either being an aerated static pile, in-vessel, windrow, aeratredwindrow or static pile type. Trends involving yard debris composting, paper addition to mixes, more organized public acceptance effort and the increase in the role of private companies in composting municipal sludge were prevalent in the survey. Odor control and marketing are still the primary management concern.

Parallel and serial methods of distributing septic tank effluent were compared using representative soil columns. Effluent was applied to each column for a period of 63 weeks. Weekly samples of renovated effluent were evaluated for volume, COD, nitrogen, phosphorus and fecal coliform content. Although both methods of distribution allowed the soil to adequacy transmit the effluent, parallel distribution increased renovation efficiency. Discharges of poor quality effluent corresponded with periodic high water-discharge-rate episodes observed only for serial-loaded columns. These episodes and the associated reduction in renovation efficiency suggest that filter fields with serial distribution have greater potential for polluting the groundwater than do filter fields with parallel distribution.

The City of Los Angeles agreed to settle with the U.S. Environmental Protection Agency (EPA) and other parties that require the city to spend an upward of $2 billion to reduce the frequency and volume of sewage spills from its sprawling collection system. Los Angeles will rebuild atleast 488 mi of sewer lines, clean 2,800 mi of sewers annually, improve its efforts to control discharges of grease from restaurants, increase the capacity of its sewer system, and draw up plans for future expansion.

Effluent entering a soil absorption system may contain varying combinations and amounts of potential contaminants. A vertical separation distance of 24 inches between the bottom of a soil absorption system and the seasonally high water table has been suggested as a minimum soil depth for proper treatment of effluent and protection of groundwater. Depth to the wet season water table can be monitored with observation wells or can be estimated from soil morphological characteristics. Caution is advised when evaluating artificial drainage as a method to improve performance of on-site sewage disposal systems.

An approach is presented for the numerical optimization of low-pressure membrane filtration processes. A multidimensional optimization of an ultrafiltration system is formulated for cost minimization and numerically solved for key optimal design and operating variables. Hollow-fiber ultrafiltration operation under steady-state conditions is assumed and optimized with respect to fiber radius, fiber length, crossflow velocity, transmembrane pressure, and system recovery. Optimizations are performed over variable raw water conditions using a sequential quadratic programming (SQP) algorithm. For typical small to moderately sized low-pressure membrane facilities ([approximately equals] 1 mgd), optimal fiber design and membrane system operation is predicted to be largely influenced by the characteristic dominance of capital costs over operating costs. Thus, total treatment costs tend to be optimal at values of decision variables where permeate fluxes are maximized, within the constraints prescribed by the system, and assuming a fixed membrane cost per unit area. For raw waters demonstrating apparent to significant membrane fouling, optimal membrane treatment is predicted to be achieved by using relatively narrow hollow fibers and relatively high crossflow velocities. For relatively clean raw waters demonstrating very high sustainable permeate fluxes, operating at low crossflow velocities--or perhaps even under the dead-end mode of operation--appears to provide the most cost-effective operation.

John Little and Benito Marinas have concluded that cross-flow air stripping suffers from the high cost of off-gas treatment. However, they failed to assess the implications of off-gas treatment. They were correct in claiming that the quantity of air used in a configuration that minimizes pumping and blower costs should be minimized. On the other hand, systems which require off-gas treatment, gas flow should be reduced and the capacity of the air for holding the pollutant should be maximized.

Bruce I. Dvorak and Desmond F. Lawler claim that cross-flow stripping is not an economically-viable alternative in the subsequent treatment of off-gases. However, the cost of off-gas treatment is equal to or greater in magnitude than the tower cost when the optimum stripping factor is forced to the minimum allowable value of two for both cross-flow and counterflow towers. The off-gas cost is the same for both configurations since the volumetric air flow rates are equal under these conditions.

In this study, the applied liquid pressure was used to characterize the rate and extent of activated sludge dewatering in the expression phase. By characterizing the liquid pressure, three important features of expression phase dewatering were determined. First, as the depth of sludge cake increased, the ability to express water from the sludge cake was greatly reduced. Second, iron and lime were found to be superior to polymer, especially as the applied pressure increased. Third, for either type of conditioner, increased pressure resulted in a decreased rate of expression. This was probably due to the highly compressible nature of activated sludge, which responds to pressure by becoming less porous.

Conventional septic system leachfields normally have been constructed utilizing gravelfilled trenches or beds. A number of alternative systems have evolved in various geographic regions. Several research workers have questioned the use of gravel in such systems, confirming concerns expressed by regulators based on field experience. Chamber-type leaching systems offer an effective alternative without the potential drawbacks of other systems.