Journal of Environmental Engineering

Studies were conducted to determine how the concentration of a chlorinated aliphatic affects acetate utilization rates and its own transformation in methanogenic systems. In these experiments, the chlorinated aliphatics used were dichloromethane (DCM), chloroform (CF), and 1,1,1-trichloroethane (TCA). Experiments were conducted in batch systems using acetate-enrichment cultures maintained at 20°C. Cultures had been exposed to these chlorinated aliphatics for approximately 2 years prior to these experiments. All three compounds were found to inhibit acetate utilization. DCM was the least inhibitory, CF the most. An uncompetitive inhibition model described DCM and TCA inhibition, with inhibition constants of 8.0 mg/L and 0.5 mg/L, respectively. CF inhibition appears to result from a more complex inhibition mechanism. CF and TCA were also found to be toxic to their own transformation, with CF being more toxic than TCA on a mg/L basis. DCM transformation in batch systems was not observed, despite previous acclimation to DCM.

Studies using batch cultures and continuously fed attached-growth systems investigated the effect of mixtures of chlorinated aliphatics on the anaerobic biotransformation rates of individual components of the mixture. Dichloromethane (DCM), chloroform (CF), and 1,1,1-trichloroethane (TCA) were selected for study because of their frequent detection in groundwater. Biotransformation of CF and TCA occurred in all systems. When CF and TCA were fed together, transformation rates for both aliphatics were lower than when fed individually. DCM generally had minor to negligible effects on the transformation of CF and TCA, but in one case, it caused a slight but statistically significant decrease in TCA transformation (p = 0.05). DCM transformation was not observed when fed individually or in mixtures to batch resting cultures, so the effect of CF and TCA on DCM transformation could not be determined.

Curbside collection of compostable material can be expensive because the inherent costs of curbside collection are high, but also because amounts collected per residence are small compared to the total waste stream, and time is wasted driving by residences at which no material is set out. In this paper, a model is presented capable of estimating route time based on the set-out rate and distribution, the amount of materials collected, and collection method characteristics. The model separately estimates travel time, collection time, and time spent waiting at stop signs and traffic lights. Model parameters are based on observation of compostables collection. Over six collection days for a collection route in Norman, Okla., the model estimated route time to within 4.8% of observed values.

Curbside collection of compostable material can be expensive because the costs of curbside collection are high, but also because amounts collected per residence are small compared to the total waste stream and time is wasted driving by non–setting-out residences. In this paper a simulation model is used to investigate the effect of collection method and route characteristics on route time. Simulation analyses indicate that route time (RT) varies almost linearly with set-out rate (SOR), the percentage of residences placing materials out on a given day. Route time per unit (RTU) of material collected remains relatively constant for higher SORs, but increases rapidly as SOR decreases below a certain point. The characteristics of the collection method and neighborhood can significantly effect RT and RTU. However, set-out distribution appears to have little effect over a SOR of approximately 5%. Thus, a simple procedure for estimating route time is presented which, coupled with a method for estimating collection needs, can be used to estimate vehicle and labor requirements for compost curbside collection programs.

Conventional location/allocation models for solid-waste management usually focus on economic optimization with respect to mass balance, capacity limitation, operating, and financial constraints. But the siting of important facilities, such as landfills, incinerators, and transfer stations, in a solid-waste management system still involves several explicit limitations that must be considered through the use of optimization techniques. This paper presents a sustainable waste management strategy in which the decision makers and the environmental analysts may put forward their views on the assimilative capacity of two major environmental factors: noise control and traffic congestion. A mixed integer programming model with the framework of dynamic optimization still can be used efficiently to achieve this goal. The practical implementation is assessed by the case study of the Kaohsiung solid-waste management system in Taiwan. It shows that the incorporation of these two environmental factors does alter the conventional waste-flow pattern in metropolitan solid-waste management systems.

This paper describes work aimed at investigating the physico-chemical factors influencing the fluorspar dissolution kinetics, with the objective of evaluating the feasibility of fluorspar as a source of water fluoridation. Experimental results indicated that under optimum conditions effluent fluoride concentrations well above 2 mg/L were obtained. However, fluoride concentrations can be reduced to below practical levels at temperatures less than 20°C and hardness greater than 100 mg/L as CaCO ₃ . By treating fluorspar as a blend of CaF ₂ and CaCO ₃ , the kinetic characteristics of fluorspar dissolution were accurately described by a steady-state mass-transfer model. Basic operating parameters for continuous fluoridation using a natural fluorspar-packed bed were investigated and the optimum conditions established. This study demonstrated that water fluoridation with natural mineral fluorspar can be more practical for small communities located in warm climates with soft-water sources.

Zebra mussel ( Dreissena polymorpha and D. bugensis ) fouling has increased operating and maintenance costs for marine and industrial facilities. An understanding of zebra mussel attachment strength on various substrates of different surface roughness is useful for the development of control strategies. Mussel attachment strength was inferred directly through tensile loading experiments using a calibrated force scale, and indirectly through fluid detachment using a wall jet. The results of both techniques were consistent and yielded statistically significant differences for different substrate types (natural ≥ metallic > polymeric). Attachment varied significantly with material ( P < 0.01) and with surface roughness within a material ( P < 0.05). The lowest attachment strengths were measured on (in increasing order of attachment strength) smooth polytetrafluoroethylene, polymethylmethacrylate, and aluminum. The strongest attachment was measured on rough limestone/dolomite cobble, and mild steel of all roughnesses. Zebra mussel attachment strength was intermediate on, marine concrete, marine plywood, polyvinylchloride, stainless steel, and coal tar epoxy coated mild steel. These results provide preliminary design guidelines for the control of zebra mussels.

The impact of effluent algae and nitrification in the BOD ₅ test on the performance of aerated lagoons is discussed, as well as ways of improving the performance. Toward this end, suggestions are made for modifying the procedure outlined in earlier papers for the design of dual-power, multicellular (DPMC) aerated lagoon systems. Such modification includes the use of the following: (1) A steady-state model for the hydrolysis of the particulate fraction of influent biodegradable materials; and (2) a steady-state algal growth model. Parameter values are suggested, and a general approach to applying the models in the design procedure is given. It is concluded that the modifications should improve performance with respect to effluent quality, and that further evaluation of performance data will be required to test the assumptions made in applying the models.

A convective-diffusion model was developed to predict the performance of both electrodialysis (ED) and adsorption on species in an aqueous solution. The quasi–steady-state model was solved by finite difference to assess the effects of a packed bed of graphite on separation of an univalent electrolyte and an organic compound in an ED cell. A sensitivity analysis of parameters in the model was also performed. Comparison of simulation results with experimental data of 2-Naphthol (2-C ₁₀ H ₇ OH) in sodium chloride solution was used for this case study. The model satisfactorily predicts 2-Naphthol removal at the 95% confidence level.