Dewatering and drying characteristics of water hyacinth (eichhornia crassipes) petiole

Abstract

Water hyacinth has become a sort of menace in several lakes, rivers and dams in Africa, especially Kenya. This has lead to the accumulation of large mounts with high moisture content and very low drying rates; hence there is a need to investigate the behaviour of water hyacinth subjected to a two stage process comprising of dewatering and drying so as to provide data that would influence design of suitable dewatering and drying equipment for water hyacinth. The broad objective of the study was to identify and relate the parameters that are important in dewatering and drying of water hyacinth petiole. This involved identification of the pertinent properties that influence dewatering and drying of water hyacinth petiole and then developing predictive empirical equations for the identified factors. Field work involved collection of samples from four different locations within Nairobi dam. The experimental design enabled a series of experiments to be carried out using a triaxial system to obtain the dewatering data and behaviour of the stress versus strain rate curves, while drying was done using a standard oven to obtain the drying data and the subsequent drying curves. Properties of water hyacinth petiole thought to be pertinent to dewatering and drying characteristics were identified and mathematical predictive equations developed from them. The relationship between deviatoric stress (q) and rate of expelled fluid (w) had a general upward exponential trend. Power series was utilized to model the behaviour of deviatoric stress versus strain rate depicting decreasing strain rates during dewatering. The average moisture content of fresh water hyacinth petiole was 91% wet basis. Mean volume of expelled fluid during dewatering was 20.66 ml (SO = 3.5, n = 16) as at the point of sample failure. Lowest strain rate at which deviatoric stress began to accumulate in the sample was around 1.2 n', while the highest was 1.5 n:'. Mean deviatoric stresses required for expelled fluid to be realised were 20.85, 34.90, 29.75 and 28.19 kPa at confining stresses 300, 400, 500 and 600 kpa. Respective standard deviations were 4.33, 5.09, 7.90 and 2.82 kPa. Mean drying rate constant -(kmean) derived from the experimental data was used to develop predictive equation that adequately described the effect of varying both drying temperature and moisture content, on time, of samples during the drying process. kmean was found to be 2.22, 2.71 and 3.39 n:' for oven drying temperatures of 105, 130 and 150°C respectively. It was evident that increasing the drying temperature resulted in an increase in drying rate whereas a change in the moisture content of the sample before drying, did not affect the drying rate at a constant drying temperature with a P-value of 0.97 at a significance level of 0.05. Statistical investigation showed that there was no significant difference in the means of the initial moisture content (P-value=0.94) for the samples collected at the four locations within Nairobi dam. The comparison between deviatoric stress and both rates of expelled fluid and strain rates further indicated that the predictive equations described both dewatering and drying characteristics of the samples accurately, with P-values above 0.50), for the range of identified pertinent parameters. The results of this research work will be useful in the design of suitable dewatering and drying equipment, as a means of solving the problems caused by high moisture content when handling and processing water hyacinth petiole as a resource.