THE EFFECTS OF IMPROVING SEWAGE SLUDGE DIGESTION

A model was developed and tested to investigate the effects of various parameters on the processing costs of anaerobic digestion. The model was based on empirical data collected from full-scale plants which varied in size from 35,000 to 900,000 population equivalents. (Equivalent to loading rates of 0.5 to 2.7 kg VS/m³/d.) In spite of different operating regimes and conditions of the plants analysed, various relationships were discovered between: sludge quality and volatile solids destruction; sludge quality and biogas yield; and, effluent volatile solids and dewatering. Where correlations existed, these were used to make predictions on operating costs of the digestion and dewatering plant based on sensitivity analysis. The results of the model were used to make recommendations on how to optimise the operation of an anaerobic digestion plant.     

Design Water Levels in Tidal River Systems under the Influence of Typhoons

Water levels in tidal rivers are subject to the influence of both fluvial and tidal factors. The interaction between these factors is rendered more complex in regions affected by typhoons, which typically result in the combined occurrence of heavy rainfall and high sea levels.
Previous studies have outlined an analytical approach for calculating design water levels based on dividing the fluvial and tidal series into a typhoon and a non-typhoon component. This paper illustrates the steps involved in the analytical approach and describes its application to drainage basins in Hong Kong.
The approach provides a practical means for calculating design water levels, and is recommended for final design purposes. The results of using the full analysis may be approximated by using a sub-set of analytical results, and should prove satisfactory for the purposes of outline design.     

Oxygen consumption and activity of the white sucker (Catostomus commersoni), in lethal and nonlethal levels of the organochlorine insecticide, methoxychlor

The survival, oxygen consumption and spontaneous activity of suckers were determined at 15°C in water containing different concentrations of methoxychlor in ethanol, ethanol, and no added substances. A dynamic bioassay was used to estimate the 96 h LC50, which was found to be 0·0345 ppm. Routine oxygen consumption was determined in a continuous-flow respirometer, and the activity was recorded in separate experiments by measuring the water disturbance using silver wire electrodes.After 24 h fish exposed to untreated, ethanol-treated and 0.01 ppm methoxychlor-treated water had oxygen uptake rates which were relatively constant and near standard levels. At 0.10 ppm methoxychlor (lethal to all fish within 85 h), oxygen consumption rates were 2–3.5 × as high as those of control fish. Activity also greatly increased. The fish lost their balance along with the coordination between opercular and locomotor movements. Suckers that died in 0.04 ppm methoxychlor showed oxygen uptake rates and poisoning symptoms similar to 0.10 ppm treated fish, while those that survived this treatment had rates similar to control fish. The increase in ventilation which accompanies this hyperactivity may result in increased uptake of insecticide and thereby explain the irreversible nature of the response.     

Geomechanical model simulation for the varied rock formations of the Kadana dam foundation,Gujarat, India

Bulletin of Engineering Geology and the Environment - Precambrian layered rocks consisting of quartzites, phyllites and metagreywackes of the Aravallis having a large variation in thickness,...     

Rapid enumeration of water bacteria

The research reported in this paper is devoted towards the development of a rapid bacteriological test for water. The proposed technique consists in measuring “Cold T.C.A. insoluble portion” of metabolized phosphorus in multiplying bacterial cells with recourse to radioactive phosphorus-32 as a tracer and enumerates bacteria in 1 h incubation time. A linear correlation (coefficient of correlation = +0·989) has been shown to exist between this portion of phosphorus and cell population for bacterial species of public-health significance, thereby providing a point d'appui for this approach of enumerating water bacteria.The data reported in the paper reveal a promise for the differential enumeration of Grams positive and negative cells by incorporating suitable chemical inhibitors in appropriate concentrations in the test portions for rapid test.The technique has been exhibited to be applicable to field samples drawn from surface and underground sources of water. Its reproducibility and economics are comparable with “Standard Method” procedures.     

Sorption of benzenesulfonates by weak base anion exchange resins

Weak base phenol formaldehyde anion exchange resins were found to have an excellent capacity for removing the anionic organic species benzenesulfonate (BS), p-toluenesulfonate (PTS) and dodecylbenzenesulfonate (DBS) from pH 2 and 4 solutions. The capacity for DBS was generally greater than that of activated carbon and significantly greater than that of a polystyrene-divinylbenzene resin with no ion exchange functional groups. The maximum capacity of the weak base resins appeared to be limited by the exchange capacity of the resin. The mechanism of removal was strongly indicated as being either ion exchange at the amine functional groups in the acid form, or uptake of a proton by the amine groups in the free base form with the organic anion as the associated counter ion. Increasing concentrations of Cl⁻ decreased the amount of organic anion that could be sorbed.The swelling of one of the resins, Duolite A-7, also had a marked effect on its sorption capacity. The pores of the acid chloride or acid organic anion form of the resin were apparently larger than those of the free base form; thus, as conversion of the resin to the acid form took place, a greater amount of uptake was observed. The effect of swelling on the capacity of Duolite S-37 was much less, apparently owing to its larger pore structure, but its capacity for DBS at low pH was lower than that for A-7 because of its lower nitrogen content. Also, BS and DBS were easily removed from the weak base resins by washing them with NaOH. Four bed volumes of 1 m NaOH gave essentially complete regeneration of BS saturated A-7.     

Dynamic analysis and optimal feedback control synthesis applied to biological waste treatment

The dynamics and optimal feedback control of biological waste treatment processes are examined. Modern feedback control theory is applied and results are obtained for both proportional and proportional plus integral control. A dynamic mathematical model of the system is developed by employing a Monod kinetic model, which is modified to account for endogenous metabolism, and a complete mixing flow model in the growth chamber. The feedback control is implemented via the flow rate so as to maintain desired effluent concentrations. External disturbances which cause changes in substrate concentration and/or cell concentration are considered and optimal control effort is applied. Results are also presented for impulse and step changes in the influent substrate concentration. It is found that by changing the values of the weighting factors in the objective function, it is possible to obtain good control of either the effluent substrate concentration or cell concentration.     

Coagulation dynamics of fractal flocs induced by enmeshment and electrostatic patch mechanisms

The size and structure of flocs during floc formation were monitored for various coagulation mechanisms. Two distinctive mechanisms, namely, enmeshment and electrostatic patch, govern the dynamics of kaolin particles coagulation by polyaluminum chloride (PACl). They were investigated by small angle static light scattering (SASLS) and solid-state ²⁷Al NMR. In addition, a novel wet SEM (WSEM) was used in-situ to image the morphology of the aggregate in aqueous solution. Synthetic suspended particles were coagulated by two PACl products, a commercial product (PACl) and one laboratory product (PACl-E). The PACl-E contained more than 60% Al₁₃ while the PACl contained only 7% Al₁₃, with large percentage of colloidal Al. For coagulation by PACl at neutral pH and high dosage where the strong repulsion between particles occurs, the enmeshment ruled by reaction-limited aggregation (RLA) results in larger sweep flocs as well as higher fractal dimensional structure. For coagulation by PACl-E at alkaline pH and low dosage, the flocs were coagulated predominately by electrostatic patch with Al₁₃ aggregates. At such condition, it is likely that diffusion-limited aggregation (DLA) predominately rule PACl-E coagulation. The fractal dimension (D_s) values of PACl and PACl-E flocs formed at enmeshment and electrostatic patch increased with dosage, respectively. When breakage of flocs occurs, the breakage rate of PACl-E flocs is slower than that of sweep flocs. By WSEM imaging, the adsorption of spherical Al precipitates onto the particles was observed to form sweep flocs with a rough and ragged contour, while the PACl-E flocs were formed with a smooth and glossy structure.     

Damage costs produced by electric power plants: An externality valuation in the Mexico City Metropolitan Area

This paper presents an estimate of the externalities produced in the Mexico City Metropolitan Area (MCMA) through the impacts on health caused by secondary pollutants attributed to seven electric power plants located outside this area. An original method was developed to make possible a simplified application of the impact pathway approach to estimate the damage costs in the specified area. Our estimate shows that the annual costs attributed to secondary pollutants total 71 million USD (min/max 20/258 million USD). Finally, this paper discusses basic ideas on the implications for energy policy arising from this exercise in externality valuation.