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Slow sand filters (SSFs) are probably the most effective, simplest and least expensive water treatment process. Micro-organisms and other particulate materials are effectively removed by SSFs. Considerable development has been done on SSFs with respect to particle removal, but only a few works have been reported in the context of the removal of heavy metals which are a severely toxic pollutant of surface waters. No extensive laboratory or pilot studies have been carried out to determine the performance or the mechanisms of removal of heavy metals by SSFs. This research is concerned with an experimental investigation of the removal of heavy metals from surface water by SSFs. Four laboratory scale SSFs were built and run according to standard design criteria. Removal of four common heavy metals [copper (Cu), chromium (Cr), lead (Pb) and cadmium (Cd)] were monitored. The filters were fed synthetic water made from tap water mixed with settled sewage, and each filter was dosed with one of the heavy metal salts. The concentrations of Cu, Cr, Pb and Cd in the influent were selected as 10 mg/l, 100 μg/l, 60 μg/l, and 100 μg/l respectively considering their relative toxicity and WHO guidelines in drinking water. Settled sewage was added to vary the total organic carbon (TOC) of the feed water. The reduction of heavy metal concentrations were monitored at various TOCs, filtration rates and filter bed depths. The results showed that SSFs succeeded in removing heavy metals from water. The removals of Cu, Cr, Pb and Cd at the conventional flow rate and filter depth are 99.6,97.2,100 and 96.6 % respectively. The results also showed that an increase in TOC in the feed water improved metal removal while increases of flow rates caused a decrease of the removal of metals. The removal of heavy metals also decreased with a reduction in sand bed depth. The optimisation of design parameters for SSFs for the removal of heavy metals depends on the individual heavy metal and on the TOC content of the feed water. Model equations were developed for, and linear correlation was observed between each of the three control parameters and the removal of the selected metal. The removal of heavy metal by SSFs was achieved through the combination of a number of mechanisms. Settlement, adsorption to both sand and organic matter and microbial

We develop three models for the flow in an estuary. The first being a 2 1-dimensional time-periodic model of a flow in the vertical cross section. The second model adds a third un-coupled velocity field U, in the along-estuary direction. The final model is a 3 + 1-dimensional, fully-coupled, time-periodic flow. We study the transport of material in each model using what are called lobe diagrams. Such diagrams allow us to separate the flow into different regions and then calculate the transport of material between adjacent regions. We also study the presence and bifurcations of curves which form partial barriers (ie. cantori and barriers formed from segments of unstable and stable manifolds of hyperbolic periodic points) or complete barriers (ie. KAM curves and other invariant circles) to transport. We use these models to develop an understanding of both the mixing within the flow and the formation and leakage of patches of higher concentration within a cloud of pollution released into the estuary. We also study the time taken for particles to exit the bounds of the estuary. As a result we get an understanding of which regions of the flow flush pollution out of the estuary in the least time and out of which end of the estuary they flush the pollution. We apply this understanding, and that gained from studying the mixing and formation of patches, to the problem of the optimal discharge of effluent into an estuary.

Fresh water is one of the most important natural resources. However, like other natural resources, the usable water is limited while the demand for water increases as industrialization proceeds and the population grows. What makes matters worse is that water resources are being reduced by pollution. Groundwater is an important water resource. However, in many countries, it has not been fully developed yet, either because of sufficient surface water sources, technical problems, or geographical conditions. Generally groundwater is relatively clean and is better protected from pollutants than surface water. Thus groundwater is an important subject for water engineers and scientists who have focused on its development and protection. In both cases, research into the movement of pollutants plays an important role in the effective exploitation of groundwater. Recently hydrologists concerned with groundwater pollution have studied multiphase flows in the subsurface because many pollution problems are characterized by multiphase contamination. The simplest multiphase pollution problem is solute transport in the unsaturated zone. More complex multiphase pollution problems involve organic matter such as petroleum products discharged to use oil. Since many of organic products are essential to our normal life and industry, the potential for groundwater pollution by them is significant unless they are controlled properly. In multiphase problems, the organic compounds may form their own flows that are distinct from the subsurface water flow but partly dissolve with the water phase and cause low concentration long term pollution of the water phase. There have been many efforts dedicated to predicting the movement of pollutants. A lot of mathematical and numerical models have been developed with the aid of laboratory and field works. However almost all models have been developed to solve a few restricted scenarios. Model users are obliged to invest considerable time in understanding the various models; their numerical accuracy and coding.The purpose of this study is to categorize the pollution patterns in the subsurface and to develop a numerical model that can be applicable to a wide variety of subsurface contamination. The general primary variables and generalizing procedures are employed to make the numerical model applicable to various pollution patterns. Many kinds of tracers can be used to know the behaviors of fluid phases in the subsurface. Because the model is able to describe partitioning of mass of a component among fluid phases, tracer problems also can be simulated by the model.

Urban sewerage systems, which are normally used for the transport of wastewater from its origin to a wastewater treatment plant (WWTP), could be used as a treatment facility because (i) they contain heterotrophic bacteria capable of oxidising organic matter both suspended within the body of the flowing wastewater and attached to the surface of the wetted perimeter, and (ii) they provide retention times which are often comparable to those in a conventional activated sludge aeration tank and which, in some cases, may be equal to the hydraulic retention time in a WWTP. Using sewers as a treatment facility could be an economical method of alleviating the load on an existing WWTP or reducing the size of the proposed WWTP. The current study was undertaken to investigate the feasibility of using urban sewerage systems as suspended growth biological reactors for the treatment of domestic wastewater. The flow in a linear gravity sewer was simulated using a batch reactor fed with raw domestic wastewater. A comparison of simulated aerobic and anaerobic gravity transport indicated that aerobic treatment would be the most favoured method of in-sewer biological treatment. The soluble COD (SCOD) removal efficiencies over a retention period of 8 hours averaged 36 and 6% under aerobic and anaerobic conditions, respectively, at an average temperature of 22°C. The corresponding total COD removal averaged 8 and 11%, respectively. When the effluent samples, taken from the batch reactors after a retention period of 6 hours, were settled in a bench-scale settling column for one hour, the average suspended solids removal under aerobic conditions was 29% greater than those under anaerobic conditions. Under aerobic conditions, the removal of soluble organic matter during simulated gravity transport was found to be strongly influenced by the strength of the incoming wastewater. To investigate the effect of wastewater influent soluble COD (SCOD 0) and influent suspended solids (SS ()) on in-sewer aerobic treatment, 27 individual wastewaters collected from the inlets to three wastewater treatment plants were subjected to batch tests at 20°C. The SCOD over a retention period of 8 hours at 20°C averaged 48, 40 and 61% for wastewaters having low SCODo and low SS 0, high SCOD0 and low SS 0, and high SCOD0 and high SSo, respectively . The corresponding soluble BOD5 removal efficiencies averaged 64, 59, and 81%. A statistical analysis of soluble COD data revealed that, over a retention period of one to three hours, the soluble COD removal is only significantly influenced by SSo. At higher retention periods, the soluble COD removal was found to be significantly affected by both SCOD 0 and SSo. Soluble COD removal was found to follow first-order kinetics with respect to time. The oxygen uptake rate of the individual wastewaters varied widely and did not appear to show any clear relation with the SCOD0 or SSo. An increase in the suspended biomass of the wastewater by the addition of activated sludge, at a concentration as low as 100 mg VSS/1, at the inlet of the simulated aerobic gravity sewer resulted in a significant increase in the removal of soluble organic matter. The soluble COD removal in the seeded wastewater was found to increase almost linearly with the increase in seed concentration in the range of 100-1000 mg/l. The effect of seed concentration on soluble COD removal however, appeared to diminish with the increase in retention time. SCOD removal in the seeded wastewater appeared to follow secondorder kinetics with respect to time. At an initial seed concentration of 100-1000 mg/1, the batch reactor's effluent after a retention period of 6 hours showed satisfactory settling characteristics. The oxygen uptake rate of the seeded wastewater did not show any specific trend over time at seed concentrations of 100 and 250 mg/1, while at higher seed concentrations it was similar to that observed in a typical plug flow activated sludge aeration tank. The results of the case study in which the wastewater collected from the inlet of the Greater Amman Siphon (GAS) was maintained aerobic in a batch reactor, showed that by maintaining aerobic conditions in the GAS, average SCUD and soluble BOD 5 removal efficiencies of 60 and 78%, respectively, could be achieved over 8 hours at an average temperature of 25°C. The average oxygen demand of the wastewater was estimated to be 30 mg/l.h. The result of the current study suggest a strong possibility of using urban sewerage systems as an aerobic biological reactor for the removal of soluble organic matter during transit.

It is essential that estuarine modelling and surveying are carried out simultaneously because not only does the latter provide data required by the former but also the former is verified with data from the latter. This study integrates both research subjects from the panoramic point of view, aiming at improving modelling accuracy and reliability and increasing survey efficiency. Partially stratified estuaries are the most difficult types of estuaries to be modelled, in particular, the velocity field in such an estuary. A review of two commonly used methods to determine the velocity field, i. e., theoretical method and empirical method, revealed their inadequacies in real applications. Thus, a new approach using Kriging technique was originated and was tested on a finite element model of water quality. The model was formulated using a Galerkinfinite element method and was programmed in Fortran. Comparison between the simulation results and the field measurements for a salinity intrusion showed a high simulation accuracy. It is believed that the model in combination with the new approach would be a useful tool for estuarine modelling. The generalized Kriging method ensured that the new approach would be appropriate in practice. It was also applied to the investigation of sampling stations in the partially mixed estuary of the River Tees. It is essential to know how many sampling stations should be used and how they should be positioned. Two procedures were designed for solving the survey problems. They were the procedure of overall variance and the procedure of re-estimation. These procedures were capable of quantifing the relative significance of each sampling station and detecting redundant sampling stations. The 1975 survey was investigated, and useful conclusions were obtained.

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No description available.

No description available.

No description available.