Atif Mustafa

Carbon Storage and Fluxes within Freshwater Wetlands: a Critical Review

We critically review recent literature on carbon storage and fluxes within natural and constructed freshwater wetlands, and specifically address concerns of readers working in applied science and engineering. Our purpose is to review and assess the distribution and conversion of carbon in the water environment, particularly within wetland systems. A key aim is to assess if wetlands are carbon sinks or sources. Carbon sequestration and fluxes in natural and constructed wetlands located around the world has been assessed. All facets of carbon (solid and gaseous forms) have been covered. We draw conclusions based on these studies. Findings indicate that wetlands can be both sources and sinks of carbon, depending on their age, operation, and the environmental boundary conditions such as location and climate. Suggestions for further research needs in the area of carbon storage in wetland sediments are outlined to facilitate the understanding of the processes of carbon storage and removal and also the factors that influence them.

The Integrated Constructed Wetlands (ICW) concept

The free surface flow Integrated Constructed Wetlands (ICW) concept explicitly combines the objectives of cleansing and managing water flow from farmyards with that of integrating the wetland infrastructure into the landscape and enhancing its biological diversity. This leads to system robustness and sustainability. Hydraulic dissipation, vegetation interception, and evapotranspiration create an additional freeboard at the outlet of each wetland segment and at the point of discharge, thus enhancing hydraulic residence time and cleansing capacity during hydraulic fluxes. The principal design criteria leading to adequate effluent water quality (i.e., molybdate reactive phosphorus less than 1 mg/1) from ICW are that the wetland area needs to be sized by a factor of at least 1.3 times the farmyard area and the aspect ratio for the individual wetland segments (i.e., approximately four cells) needs to be less than 1:2.2 (width to length). Within a year of ICW commissioning, approximately 75% of farmyard runoff was intercepted, leading to improvements in the receiving surface waters of the catchment. Most of the recorded phosphate concentrations after ICW treatment agreed with the Irish Urban Wastewater Treatment Regulation 2001, which can be used as a benchmark to assess ICW treatment performance and which is usually applied unofficially to ICW even if it may appear to be too stringent. A case study of 13 ICW systems suggested that phosphorus exported from an ICW system was similar to the typical background concentrations of phosphorus export rates from land to water.

The universal design, operation and maintenance guidelines for farm constructed wetlands (FCW) in temperate climates

This paper comprises the scientific justification for the Farm Constructed Wetland (FCW) Design Manual for Northern Ireland and Scotland. Moreover, this document addresses an international audience interested in applying wetland systems in the wider agricultural context. Farm constructed wetlands combine farm wastewater (predominantly farmyard runoff) treatment with landscape and biodiversity enhancements, and are a specific application and class of integrated constructed wetlands (ICW), which have wider applications in the treatment of other wastewater types such as domestic sewage. The aim of this review paper is to propose guidelines highlighting the rationale for FCW, including key water quality management and regulatory issues, important physical and biochemical wetland treatment processes, assessment techniques for characterizing potential FCW sites and discharge options to water bodies. The paper discusses universal design, construction, planting, maintenance and operation issues relevant specifically for FCW in a temperate climate, but highlights also catchment-specific requirements to protect the environment.

Assessment of the nutrient removal performance in integrated constructed wetlands with the self-organizing map

The self-organizing map (SOM) model was applied to predict outflow nutrient concentrations for integrated constructed wetlands (ICWs) treating farmyard runoff. The SOM showed that the outflow ammonia-nitrogen concentrations were strongly correlated with water temperature and salt concentrations, indicating that ammonia-nitrogen removal is effective at low salt concentrations and comparatively high temperatures in ICWs. Soluble reactive phosphorus removal was predominantly affected by salt and dissolved oxygen concentrations. In addition, pH and temperature were weakly correlated with soluble reactive phosphorus removal, suggesting that soluble reactive phosphorus was easily removed within ICWs, if salt concentrations were low, and dissolved oxygen, temperature and pH values were high. The SOM model performed very well in predicting the nutrient concentrations with water quality variables such as temperature, conductivity and dissolved oxygen, which can be measured cost-effectively. The results indicate that the SOM model was an appropriate approach to monitor wastewater treatment processes in ICWs.

Application of the self-organizing map as a prediction tool for an integrated constructed wetland agroecosystem treating agricultural runoff.

A self-organizing map (SOM) model was applied as a prediction tool for the performance of an integrated constructed wetland (ICW) agroecosystem treating agricultural runoff to protect receiving watercourses. By utilizing the SOM model, the time-consuming to measure expensive biochemical oxygen demand outflow concentrations were predicted well by other inexpensive variables, which were quicker and easier to measure. Correct predictions for the outflow biochemical oxygen demand concentrations were between 89% and 100%. This novel approach allows for the real time control of the outflow water quality of the ICW and potentially also of other treatment system applications. Moreover, the missing values and outliers from the large but incomplete ICW data set were replaced accurately by most likely values determined by the SOM model. This was important because the proportions of unusable entries for chemical oxygen demand, suspended solids and biochemical oxygen demand were very high: 41%, 54%, and 61%, respectively.

Application of solar disinfection for treatment of contaminated public water supply in a developing country: field observations

A sustainable and low-cost point-of-use household drinking water solar disinfection (SODIS) technology was successfully applied to treat microbiologically contaminated water. Field experiments were conducted to determine the efficiency of SODIS and evaluate the potential benefits and limitations of SODIS under local climatic conditions in Karachi, Pakistan. In order to enhance the efficiency of SODIS, the application of physical interventions were also investigated. Twenty per cent of the total samples met drinking water guidelines under strong sunlight weather conditions, showing that SODIS is effective for complete disinfection under specific conditions. Physical interventions, including black-backed and reflecting rear surfaces in the batch reactors, enhanced SODIS performance. Microbial regrowth was also investigated and found to be more controlled in reactors with reflective and black-backed surfaces. The transfer of plasticizer di(2-ethylhexyl)phthalate (DEHP) released from the bottle material polyethylene terephthalate (PET) under SODIS conditions was also investigated. The maximum DEHP concentration in SODIS-treated water was 0.38 μg/L less than the value of 0.71 μg/L reported in a previous study and well below the WHO drinking-quality guideline value. Thus SODIS-treated water can successfully be used by the people living in squatter settlements of mega-cities, such as Karachi, with some limitations.

Characterization of Microbial Communities Transforming and Removing Nitrogen in Wetlands

The community structure of bacteria responsible for transformation and removal of nitrogen species from farmyard runoff within two different full-scale integrated constructed wetland (ICW) systems was studied. Microbial communities in litter and sediment components were investigated using denaturing gradient gel electrophoresis (DGGE) and band sequencing of the 16S ribosomal ribonucleic acid gene fragments of putative ammonia-oxidizing bacteria and the nitrite reductase genes (nirK/S) of putative denitrifying bacteria. Findings show that retrieved sequences of ammonia-oxidizing bacteria communities in litter samples were related to Nitrosomonas and Nitrosospira, while those from sediment samples were related to only Nitrosospira. A more diverse denitrifying community was present in the litter compared to the sediment samples. Non-metric multi-dimensional scaling analysis showed that microbial communities were readily distinguishable with respect to site and source (sediment and litter) for the two representative example ICW systems. A comparison of the species composition of the ammonia-oxidizing bacteria and denitrifiers in the systems revealed that the communities were no more similar or dissimilar than if they had been assembled by chance.