Treating municipal wastewater with the goal of resource recovery.

A new municipal wastewater treatment flowsheet was developed with the objectives of energy sustainability, and water and nutrient recovery. Energy is derived by shunting a large fraction of the organic carbon in the wastewater to an anaerobic digestion system. Aerobic and anaerobic membrane bioreactors play a key role in energy recovery. Phosphorus and nitrogen are removed from the wastewater and recovered through physical-chemical processes. Computer modeling and simulation results together with energy balance calculations, imply the new flowsheet will result in a dramatic reduction in energy usage at lower treatment plant capital costs in comparison to conventional methods.

A balancing act: the consulting engineers' pragmatic view of process modelling.

Modelling: what do we know, what do we want to know and why? The practical application of models to real projects is often circular because these questions weren't asked prior to making the decision to model the plant under study. Modelling wastewater treatment plants can provide insight into the inner workings of the process that might not be attainable any other way, but is that added process knowledge always needed or necessary and what criteria does one use to determine the level of effort required? These complex modelling decisions require education, communication, and improved understanding amongst both modellers and clients. This submission explores the use of models by consultants for consulting purposes and the balancing acts (time versus knowledge and cost versus benefit) that the consulting engineer must manage when embarking on any modelling project.

Effect of bubble-induced surface turbulence on gas-liquid mass transfer in diffused aeration systems.

Models that predict volatilization of organic compounds from wastewater treatment basins may underestimate emission rates if the surfaces are considered as quiescent. In reality, the water surface may be agitated by subsurface aeration, increasing mass transfer across the tank surface air-water interface. This study investigated the effect of turbulence, induced by diffused bubble aeration, on mass transfer at the water surface of a pilot aeration basin. The mass transfer of ammonia from an enclosed headspace over the basin to acidified water was measured when different diffuser types and airflow rates were applied. Oxygen-transfer tests were conducted immediately following each ammonia-transfer test. Increasing airflow rates through fine- and coarse-bubble diffusers had a significant effect on the ammonia mass-transfer rate. Experimental mass-transfer parameters (K(L)a's) for surface volatilization derived with aeration present were up to 48% higher than the K(L)a values for quiescent conditions over the range of conditions tested. No effect of diffuser type on ammonia transfer could be determined. The study results infer an effect on oxygen transfer into the water at the surface and potential transfer of volatile organic compounds, if present, from the water. The results of the ammonia mass-transfer experiments suggest that adjustments to the existing mass transfer correlations for surface volatilization from aeration basins may be in order. Such adjustments will have the greatest effect on predictions for the less volatile compounds, under conditions of low airflow rates.

Biotechnology developments for the treatment of toxic and inhibitory wastewaters.

The cost-effectiveness of biological processes has encouraged many researchers to consider biotreatment for the stabilization of toxic or recalcitrant wastewaters. However, to ensure adequate removal of trace contaminants and satisfactory performance with high strength inhibitory industrial wastewaters, conventional biotechnology is being re-evaluated. This review summarizes selected recent contributions to the development of appropriate biotechnology for toxic wastewater treatment. Microbiological constraints and potential solutions are examined. Assessments of conventional biological processes for contaminant control are reviewed, and several new developments in bioreactor design for inhibitory wastes are presented.

Blastic transformation of lymphocytes in in vitro cultures under the influence of phytohemagglutinin and pokeweek mitogen in patients with glomerulonephritis treated over long periods of time with immunosuppressive drugs.

In vitro reactivity of lymphocytes to phytohemagglutinin (PHA) and pokeweek mitogen (PWM) was studied in 17 patients with chronic glomerulonephritis treated systematically over many months (average, 23 months) with immunosuppressive drugs (prednisone, indomethacin, azathioprine, cyclophosphamide). Blastic transformation of lymphocytes in cultures stimulated with PHA was tested three times: before beginning of treatment, during the course of therapy with full doses, and after prolonged ambulatory treatment with maintenance doses. The degree of blastic transformation under the influence of PWM was determined only after periods of many months of treatment with chemical immunosuppresors. The results showed that neither treatment of chronic glomerulonephritis for several weeks with full doses, nor subsequent prolonged administration (for periods of tens of months) of maintenance doses of immunosuppresors regularly inhibit blastic transformation of lymphocytes stimulated with PHA. Similar observations were made using PWM after many months of immunosuppressive therapy. Reactivity of lymphocytes to PWM in all patients resembled reactivity to PHA.

Blastic transformation of lymphocytes in in vitro cultures during immunosuppressive therapy in patients with glomerulonephritis.

Blastic transformation of peripheral blood lymphocytes following stimulation with phytohemagglutinin during immunosuppressive therapy (prednisone 2 mg/kg body weight, indomethacin 2--3-5 mg/kg, azathioprine 2--4 mg/kg, cyclophosphamide 1-5--3 mg/kg per day) was studied in 59 patients with various morpholigic forms of chronic glomerulonephritis and in 7 with lupus erythematosus nephritis. No uniformly regular influence of immunosuppressive therapy in the doses employed in glomerulonephritis on blastic transformation in in vitro cultures was noted. The specific drug administered was not decisive for the character of the change in reactivity of lymphocytes (increase or decrease in blastic transformation). The interesting observation was made that efficacy of treatment was high in patients with lowest initial values of blastic transformation and its greatest increase during therapy. Apparently, disorders of cellular immunity assessed on the basis of blastic transformation of lymphocytes stimulated with phytohemagglutinin are not a decisive prognostic factor in glomerulonephritis. The results are discussed from the aspect of a possible influence of immunosuppressive therapy on restoration of the physiological proportion of T and B lymphocytes in peripheral blood.

North American performance experience with anoxic and anaerobic selectors for activated sludge bulking control.

Obtaining reliably high compaction characteristics and low SVI values has enormous economic consequences on activated sludge plant design and operation. Now that use of selectors has become more common for achieving low SVI values, the assessment of the full-scale performance characteristics of activated sludge plants incorporating selectors has high value for the design and operation of future plants. Treatment plant effluent quality is seldom analyzed solely on an average basis and the impact peak events have on effluent quality must be considered in design and operation. Descriptive statistics should also be used to assess selector performance, so that the influence of infrequently occurring values on plant design and operation can be assessed. The performance of 21 activated sludge plants incorporating selectors was evaluated. All the selector plants for which post installation data were available showed that the operating SVI values were significantly improved. One plant studied in detail showed that final effluent quality was significantly better after the selector installation. As a group, activated sludge plants with anaerobic selectors outperform those with anoxic selectors. Dissolved oxygen control is just as important in activated sludge plants with selectors as in conventional activated sludge plants.