Desalination of water can be achieved via the use of solar stills, especially as they are considered to be the cheapest option for potable water production in remote, arid and small communities with limited availability of freshwater. However, one very common challenge with water production via solar stills is that the amount of water produced is usually low. The aim of this work is to evaluate the productivity enhancement of solar stills using different heat storage materials in the basin. To conduct the experiments, three triangular solar stills were fabricated with similar shapes. In each solar still, a transparent polythene film and a stainless steel trough as cover and basin were used, respectively. Each basin had a length of 50 cm, width of 30 cm and depth of 8 cm. The solar still configurations differed based on inclusion of 2 cm depth of black soil or a layer of black paint in the basin. Experimental outputs indicated that there was significant increase in the amount of potable water produced using different heat storage materials under Malaysia tropical condition. Daily cumulative results of water production using these solar stills showed that the solar still with black-painted basin was more efficient; its level of productivity over the conventional solar still and the solar still with black soil in basin was 101 and 20 %, respectively. Some water quality parameters were also tested in the laboratory which indicated that the treated water met the WHO standard for drinking water.Keywords Solar distillation Á Stainless steel basin Á Black soil Á Black paint Á Potable water Nomenclature T w1 Temperature of water of solar still SS1 (°C) T w2 Temperature of water of solar still SS2 (°C) T w3 Temperature of water of solar still SS3 (°C) T a Temperature of ambient air (°C) T ic1 Temperature of inner cover of solar still SS1 (°C) T ic2 Temperature of inner cover of solar still SS2 (°C) T ic3 Temperature of inner cover of solar still SS3 (°C) I s Solar irradiance (W/m2) W h1 Hourly water production of solar still SS1 (L/m2) W h2 Hourly water production of solar still SS2 (L/m2) W h3 Hourly water production of solar still SS3 (L/m2) W c1 Cumulative water production of solar still SS1 (L/m2) W c2 Cumulative water production of solar still SS2 (L/m2) W c3 Cumulative water production of solar still SS3 (L/m2) V Wind speed (m/s)

2015): Sustainable potable water production using a solar still with photovoltaic modules-AC heater, Desalination and Water Treatment, A B S T R A C T Solar energy as a sustainable energy source can be harnessed to produce potable water using solar stills. In this work, effort was made to evaluate the performance of a double slope solar still integrated with a 500 W heater to produce potable water. The heater was powered by six photovoltaic modules, which can produce 1.5 KWp and then connected to four batteries with capacity of 150 Ah each. The experiments were conducted over several days in the tropical climate of Malaysia. A black painted steel trough with length 90 cm, width 45 cm, and depth 8 cm was used as the basin of the glass covered double slope solar still. A comparison of the cumulative water production between the conventional solar still (CSS) and solar still with PV-Heater (CSSPVH) was done. The CSSPVH was found to be more effective; producing about six times the amount of water produced by the CSS. Mathematical models derived based on energy balance studies of CSSPVH, were used to carry out simulations to verify the experimental findings. The energy balance equations of condensing cover and the basin water of CSSPVH were developed as well. A good agreement was found between numerical and experimental productivities of CSSPVH. An expected increase in water production of up to 16 kg/m 2 per 24 h was obtained using CSSPVH. Therefore, CSSPVH is an effective design to produce sustainable potable water, even in areas with very low daily solar radiation intensity, due to its ability to store solar energy. In addition, some tested water quality parameters indicate that water produced from solar stills meet the WHO standard for potable water.

This study investigated the water quality of some of the ex-mining lakes in Perak State of Malaysia for possible use as alternative to water supply and compared them to water quality of some of the rivers used for intake of water treatment. A total of twelve (12) water samples were collected for analyses from selected sampling sites. These samples were analyzed for physico-chemical properties, heavy metals concentrations, and organic pollutants concentrations. The analyzed results indicated that average temperature varied from 28.1 oC to 34.1 oC, pH 6.2 to 9.0, EC 55 to 400 μs/cm ,turbidity 5.6 to 74.2 NTU, DO 3.21 to 9.56 mg/l, TDS 36.8 to 268 mg/l, F- 0.017 to 0.182 mg/l, Cl- 0.483 to 3.339 mg/l, Br- 0 to 0.392 mg/l, SO42- 0.051 to 15.307 mg/l, Mg 0.833 to 1.466 mg/l, Na 0.669 to 3.668 mg/l, and Ca 2.85 to 26.77 mg/l. Heavy metals concentrations (mg/l) were: Zn 0.04 to 0.057, Pb 0.019 to 0.075, Cd not detected, Ni 0.013 to 0.105, As not detected to 0.004, and Cu not detected while COD 4 to 51 mg/l. Analyses revealed that all the water samples were turbid and containing slightly high concentration of Pb. Generally, they had common water quality problem. Further work should carry out more tests on other water quality parameters particularly on heavy metals, chemical and biological pollutants at different seasons.

Endogenous respiration processes of nitrifying/denitrifying bacteria under aerobic and anoxic conditions were investigated in a batch study using three identical bioreactors of size 5 L. The rate of digestion of microbial protoplasm was determined through the oxidation of cell tissue and the formation of new cellular materials using the Volatile Suspended Solids (VSS) method. Chemical Oxygen Demand (COD), ammonia, nitrate and VSS were monitored simultaneously at different sludge age. Three exponential phases of metabolism, starvation and death were observed during VSS reduction in both the aerobic and anoxic digestion. In the aerobic digestion, the average endogenous decay coefficient of volatile suspended solids was 0.055 L dayG 1 with a 95% confidence limit of 0.017 whereas 0.053 L dayG 1 was observed for anoxic digestion with a 95% confidence limit of 0.038 at 25±1°C. Results show that anoxic digestion has a slightly reduced decay rate than aerobic digestion. Therefore, the characterization of biomass and determination of stoichiometry coefficients is essential for understanding the activities of microbes in treatment processes.

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