Environmental conditions and the performance of free water surface flow constructed wetland: a multivariate statistical approach

During the past three decades, constructed wetlands have become an integral part of the suite of technologies for removing domestic and industrial wastewater contaminants. The use of constructed wetlands has disproportionately focused on domestic and agricultural wastewaters and storm water runoff and less on oil and gas-related produced water. In this context, the cumulative effect of environmental factors on the treatment/removal efficiency of contaminants in produced water is underserved by research. Therefore, this study assessed the effect of environmental factors (temperature, dissolved oxygen, oxidation–reduction potential, and pH) on contaminant removal efficiency in free water surface flow constructed wetland (FWSFCW) using ordinary least squares regression and experimental data from a waste treatment facility in Ghana. The results showed that environmental factors did not systematically vary across the experimental group and control set-up. Generally, the environmental factors explained relatively far less of the variance in contaminant removal efficiency compared with the plant species (Typha latifolia, Ruellia simplex and Alternanthera philoxeroides). Environmental factors cumulatively explained only 1.3%, 16.4%, 22.6%, and 5.6% of the variance in removal efficiency of BOD, COD, oil and grease, and total coliform bacteria, respectively. Temperature was the most important environmental predictor of the removal of BOD and phosphorus whereas DO was most important for removing nitrates and total coliform bacteria. ORP and pH were the most important predictors of COD, and oil and grease, respectively. These findings underscore the complex relationships among environmental factors and contaminant removal efficiency and the need for contaminant management practices and remedial techniques that address these complexities.

     

Derivation of scenario-specific water quality guidelines for acid mine drainage in South Africa,using a risk-based approach

Acid mine drainage (AMD) continues to threaten water quality in many mining regions globally. Data paucity renders it challenging to inform appropriate water quality management strategies for a succinct scientific understanding of the effects of AMD on freshwater ecosystems. The current study investigated the effects of AMD collected from a defunct coalmine in Mpumalanga, South Africa, on freshwater ecosystems using a risk-based approach on five indigenous species, Adenophlebia auriculata, Burnupia stenochorias, Caridina nilotica, Pseudokirchneriella subcapitata and Oreochromis mossambicus in 2016. Species responded differently to AMD after 96 hours and 240 hours of exposure in static experimental test designs. Burnupia stenochorias was more sensitive to AMD after 96 and 240 hours of exposure, whereas O. mossambicus was tolerant during short-term exposure, but became more sensitive after 240 hours of exposure than the other species tested. The availability of metals in AMD was directly associated with dilution rate. Scenario-specific water quality guidelines for AMD have been derived as 0.122% for short-term and 0.014% for long-term exposure. These may form important indicative dilutions for other AMDs that do not match the scenarios of this study. The toxicity of AMD to a wide range of aquatic species, including field validations, requires further investigation.     

Malaria vectors and transmission dynamics in coastal south-western Cameroon

Background

Malaria is a major public health problem in Cameroon. Unlike in the southern forested areas where the epidemiology of malaria has been better studied prior to the implementation of control activities, little is known about the distribution and role of anophelines in malaria transmission in the coastal areas.

Methods

A 12-month longitudinal entomological survey was conducted in Tiko, Limbe and Idenau from August 2001 to July 2002. Mosquitoes captured indoors on human volunteers were identified morphologically. Species of the Anopheles gambiae complex were identified using the polymerase chain reaction (PCR). Mosquito infectivity was detected by the enzyme-linked immunosorbent assay and PCR. Malariometric indices (plasmodic index, gametocytic index, parasite species prevalence) were determined in three age groups (<5 yrs, 5–15 yrs, >15 yrs) and followed-up once every three months.

Results

In all, 2,773 malaria vectors comprising Anopheles gambiae (78.2%), Anopheles funestus (17.4%) and Anopheles nili (7.4%) were captured. Anopheles melas was not anthropophagic. Anopheles gambiae had the highest infection rates. There were 287, 160 and 149 infective bites/person/year in Tiko, Limbe and Idenau, respectively. Anopheles gambiae accounted for 72.7%, An. funestus for 23% and An. nili for 4.3% of the transmission. The prevalence of malaria parasitaemia was 41.5% in children <5 years of age, 31.5% in those 5–15 years and 10.5% in those >15 years, and Plasmodium falciparum was the predominant parasite species.

Conclusion

Malaria transmission is perennial, rainfall dependent and An. melas does not contribute to transmission. These findings are important in the planning and implementation of malaria control activities in coastal Cameroon and West Africa.