Simultaneous adsorption and biodegradation of synthetic melanoidin

Molasses spent wash contains melanoidin, a dark brown recalcitrant compound. It is not easily biodegraded and causes a number of problems such as reduction in photosynthetic activities and dissolved oxygen when discharged to aqueous environment. Being an antioxidant, melanoidin removal through purely biodegradation has been inadequate. Consequently, in the current study, simultaneous adsorption and biodegradation (SAB) was employed in a stirred tank system to remove melanoidin from synthetic wastewater. Mixed microbial consortium was immobilized onto 200 g of activated carbon and used to degrade 3.5 L of melanoidin solutions with varying chemical oxygen demand (COD) concentrations. The effects of the initial COD level, pH and temperature on COD removal were then studied. Ultimately, the SAB performance was compared to that of batch adsorption or biodegradation carried out independently. After 48 h of operation, the SAB process yielded the best COD removal efficiency of 75% as compared to 49.3 and 51.9% for adsorption and biodegradation, respectively, for the initial COD value of 10800 mg/ L at a temperature of 296 K and pH 6.97. This therefore showed that the SAB process can successfully be applied to enhance the removal of melanoidin from wastewater.Key words: Adsorption, biodegradation, melanoidin, SAB, wastewater

Use of a Semi-field System to Evaluate the Efficacy of Topical Repellents under user Conditions Provides a Disease Exposure free Technique Comparable with Field Data.

Before topical repellents can be employed as interventions against arthropod bites, their efficacy must be established. Currently, laboratory or field tests, using human volunteers, are the main methods used for assessing the efficacy of topical repellents. However, laboratory tests are not representative of real life conditions under which repellents are used and field-testing potentially exposes human volunteers to disease. There is, therefore, a need to develop methods to test efficacy of repellents under real life conditions while minimizing volunteer exposure to disease. A lotion-based, 15% N, N-Diethyl-3-methylbenzamide (DEET) repellent and 15% DEET in ethanol were compared to a placebo lotion in a 200 sq m (10 m x 20 m) semi-field system (SFS) against laboratory-reared Anopheles arabiensis mosquitoes and in full field settings against wild malaria vectors and nuisance-biting mosquitoes. The average percentage protection against biting mosquitoes over four hours in the SFS and field setting was determined. A Poisson regression model was then used to determine relative risk of being bitten when wearing either of these repellents compared to the placebo. Average percentage protection of the lotion-based 15% DEET repellent after four hours of mosquito collection was 82.13% (95% CI 75.94-88.82) in the semi-field experiments and 85.10% (95% CI 78.97-91.70) in the field experiments. Average percentage protection of 15% DEET in ethanol after four hours was 71.29% (CI 61.77-82.28) in the semi-field system and 88.24% (84.45-92.20) in the field. Semi-field evaluation results were comparable to full-field evaluations, indicating that such systems could be satisfactorily used in measuring efficacy of topically applied mosquito repellents, thereby avoiding risks of exposure to mosquito-borne pathogens, associated with field testing