The effects of time and carbon height on the removal of chromium from wastewater were investigated in fixed down flow adsorption columns containing mango seed shell activated carbon (MSSAC) for the purpose of converting the waste to wealth. The Hutchin's bed depth service time (BDST) model was used to study the columns performance at 10% and 90% breakthrough concentrations. The BDST model constants were determined. The BDST equation obtained at flow rate of 1.61l.hr and influent chromium concentration of 3.151mg/L was used to predict the adsorbent performance at other flow rates and initial chromium concentrations. Results obtained revealed that there was a gradual decrease in the percentage of chromium adsorbed with time; the percentage adsorbed became zero at 72.33, 467.5 and 572 hours respectively for 3cm, 3.5cm and 4cm carbon heights. The breakthrough curves for chromium adsorption deviated from the characteristic S-curve for most dynamic studies because 100% removal of chromium was not attained even at the commencement of the column operation because of the high initial concentration of the adsorbate adopted in this study. It was observed that for a given breakthrough concentration, the service time decreased with increase in both flow rate and initial chromium concentration. Chi-square test performed on the developed BDST models revealed the reliability of the models for the prediction of the columns performance particularly at lower breakthrough concentrations. It was therefore recommended that MSSAC can be used for the removal of chromium from wastewater in adsorption columns; however there is the need for pilot studies on live wastewater to investigate the effect of interference.

The possibility of using Albizia saman pod activated carbon (ASPAC) as an adsorbent in fixed down flow adsorption columns to remove Cd (II) from wastewater was investigated for the purpose of converting the waste to a valuable product. The effects of impregnation ratio, particle size, carbon height, pressure head and initial cadmium Cd (II) concentration on the adsorption of Cd (II) from wastewater were investigated. The obtained adsorption data from the experiment was then fitted into the Hutchin's bed depth service time (BDST) model to study the columns performance at 15% and 90% breakthrough concentrations. The BDST model constants were determined. An optimal pressure head of 5 cm, impregnation ratio of 1:6, packing height of 3.5 cm, particle size of 75 µm and initial Cd (II) concentration of 0.029 mg/L were found to be the most effective combination, which removed 100 % of the Cd (II) within a service time of 14 hrs. There was a gradual decrease in the percentage of adsorbed Cd (II) with time; the percentage adsorbed became zero at 44, 56 and 86 hours respectively for 2.5 cm, 3 cm and 3.5 cm carbon heights. The breakthrough curves for Cd (II) adsorption maintained the characteristic S-curve for most dynamic studies. Chisquared test performed on the developed BDST models revealed the goodness of fit of the models for the prediction of the columns performance at all breakthrough concentrations investigated. The use of ASPAC as adsorbent for the removal of Cd (II) from wastewater in adsorption columns is therefore recommended.

Activated carbons were produced from a local variety of mango seed by carbonizing the inner seed before activation with ZnCl 2 using an impregnation ratio of 1:4. Laboratory batch studies were conducted in order to generate data for kinetic and equilibrium modelling of adsorption of colour by the produced mango seed endocarp activated carbon (MSEAC) for the purpose of determining the mechanism and rate controlling steps of the adsorption process. Langmuir, Freundlich and Tempkin Isotherms were adopted. While the kinetic models used were pseudo first order kinetic, pseudo second order kinetic, Intra-particle diffusion and Elovich models. The pseudo second order model gave the highest coefficient of determination (R 2) of 0.999 (indicating goodness of fit) compared to other kinetic models tested. This suggests that chemisorption is the rate-limiting step in this biosorption system. Langmuir isotherm fitted experimental data better compared with the other tested models(R 2 =0.9987), implying that the adsorption process is based on a monolayer adsorption. Chi-squared test performed on all the models confirmed the goodness of fit of the generated data to the Langmuir and pseudo-second order over the other isotherm and kinetic models because they had the least caculated Chi-squared (χ 2 Cal) values of 5.2 and 3.2 respectively. It was recommended that these two models are reliable tools for predicting the mechanism and rate of adsorption of colour from textile wastewater by the produced MSEAC.

This report presents the findings of the study on the determinants of residential per capita water demand of Makurdi metropolis in Benue State, Nigeria. Data for the study was obtained by the use of questionnaires, oral interviews and observations. The data was analyzed using SPSS. Twenty variables were considered in the multiple regression analysis for developing a consumption model. Seven variables were found to influence residential per capita water consumption significantly. Level of education, gender, kitchen type, number of cars, and well as a source were positively significant while, household size and number of children below 6 years influence the per capita water demand negatively. The multiple regression analysis showed R 2 of 0.434 implying that the model explains 43% of the variation in residential per capital water demand of Makurdi. The F test (F= 14.236, p= 0.01) showed that the variables in the model combine together to predict the residential per capita water demand of Makurdi metropolis. The consideration of the various factors identified as influencing the residential per capita water consumption in Makurdi metropolis is recommended.

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