- Experiences on the implementation of a pilot grey water treatment and
reuse based system at a household in the slum of Kyebando-Kisalosalo,
- Authors: Charles B. Niwagaba; Patrick Dinno, Isaac Wamala, S. Sahar Dalahmeh, Cecilia Lalander Håkan Jönsson
Abstract: Grey water constitutes the largest fraction of domestic wastewater. It causes environmental sanitation and pollution problems if it is not managed well. If treated, grey water can be a resource for a variety of uses. A pilot system was constructed in February 2013 to treat grey water from a four-member household for sub-surface irrigation of local vegetables. A hydraulic loading rate (HLR) of 60 L m−2d−1 and an organic loading rate (OLR) of 519–1,580 g BOD5m−2d−1 were implemented on a multi-media filter of gravel, charcoal, geotextile and mulch (charcoal being the predominant layer) operated as a batched type-system, with a 36-hour retention time. The system was operated for 3 months, during which it showed remarkable removal efficiencies of 90.8 ± 5.4 and 96.1 ± 3.0% after 36 hours for chemical oxygen demand (COD) and biochemical oxygen demand (BOD), respectively, and 95 ± 3.1% for faecal coliforms (FC). The removal efficiencies at 36 hours, of total nitrogen (TN), total phosphorus (Tot-P), total suspended solids (TSS) and total dissolved solids (TDS) were 39.0, 30.1, 85.2 and 78.6%, respectively. Plant response to sub-surface irrigation with treated grey water was largely masked by rainy season and the effluent had a limited effect on the soil.
- Seawater desalination as an option to alleviate water scarcity in South
Africa: the need for a strategic approach to planning and environmental
- Authors: G. O. Schreiner; R. C. van Ballegooyen W. Osman
Abstract: In the last decade, seawater reverse osmosis (SWRO) has come to be seen by policy-makers as a novel technology that will significantly advance water security in South African coastal regions. Water purveyors, from the private sector, local/district municipalities and provincial authorities, are undertaking studies to explore the feasibility of SWRO to meet growing demand and relieve mounting pressure on current bulk water supply infrastructure. With this in mind, it is suggested that national strategic planning should be introduced to present the opportunities and constraints of the desalination option within the national water and energy policy. In absence of this, piece-meal decisions will be made at local authority levels and the construction of SWRO plants will be determined by regional circumstances (e.g. drought) as opposed to national water policy agenda. This paper explores the value of such a strategy by considering the drivers of SWRO in South Africa, the risk of unplanned large-scale SWRO implementation (with a focus on environmental impacts) and the initial steps that could be taken toward a Strategic Environmental Assessment for SWRO in South Africa.
- On-farm treatment of wastewater used for vegetable irrigation: bacteria
and virus removal in small ponds in Accra, Ghana
- Authors: Andrea I. Silverman; Mark O. Akrong, Pay Drechsel Kara L. Nelson
Abstract: Many urban farmers in Accra collect irrigation water from streams and open drains, which they store in small, on-farm ponds before use. Given that this water can be highly contaminated with wastewater, another potential role of the ponds is to disinfect irrigation water prior to use. To better understand the factors influencing bacteria and virus removal in these small ponds, we investigated the removal of culturable fecal indicator bacteria (Escherichia coli and enterococci) and coliphage (F+ and somatic coliphage) in a single batch of water stored for 3 days. Sunlight exposure was found to be important for removal. Bacteria and coliphage removal rates were faster in shallow sun-exposed water than in deeper water, due to sunlight attenuation with depth. Bacteria removal rates varied depending on solar irradiation, and correlations between total daily UVB fluence and bacteria removal rates were observed. Coliphage removal was observed in sun-exposed water but not in dark controls that allowed for sedimentation, further highlighting the importance of sunlight-mediated processes. These small ponds appear to have similar disinfection processes to larger-scale waste stabilization ponds, but can have more efficient inactivation due to their shallow depth and operation as batch reactors. Design and management recommendations for on-farm ponds are discussed.
- Estimating microbial risk in treated wastewater for reuse: a case study in
- Authors: Shuang Liu; Kenneth M. Persson
Abstract: The potential microbial risk from using treated wastewater is a burning issue to be studied. In Sweden, only a small part of treated wastewater is reused directly, although water reuse could be beneficial. Disinfection is virtually never practised and no protective guidelines for water reuse are found in Sweden. Based on a 1 year monitoring programme of water quality, this paper estimates the microbial risk of Escherichia coli and rotavirus in treated wastewater for different applications of irrigation, landscape, industry, unban non-potable water. A Quantitative Microbial Risk Assessment model is used and the samples were collected from the pond system of Källby wastewater treatment plant in Lund, Sweden. The results are used to evaluate if the treated wastewater after tertiary treatment process combined with pond system can be reused for different applications from a microbial point of view. The risk assessment results show that the studied water is only suitable for agriculture irrigation, while additional treatment or disinfection are needed for other applications since the potential risks are higher than the value that can be accepted. The protective guidelines are discussed based on the process and results of risk assessment and suggestions for establishing a structure of guidelines in Sweden are presented.
- Analysis of membrane fouling by proteins during nanofiltration of chitin
- Authors: Juan Li; Liming Zhao, Yaosong Wang, Chaoqin Chen, Jiachun Zhou, Yongjun Qiu Hailong Du
Abstract: The membrane fouling mechanism used during the nanofiltration (NF) of chitin alkali effluent was investigated. Tests were carried out in three large-scale chitin-processing plants with three kinds of wastewater. An alkali resistant NF membrane with molecular weight cut-off of 250 Da was employed. The reflection coefficient (σ) and diffusion coefficient (Ps
) of total proteins were deduced, assuming that the proteins were single entities in the feed. Viscosity and osmosis pressure were measured to evaluate their influences on the permeate flux. Furthermore, the fraction of the protein fouling was extracted and qualitatively analyzed by mass spectrometry. Results showed that the NF permeate flux of alkali wastewater with the highest protein concentration (4.00%) was the lowest, and that σ and penetration Ps
decreased with protein content growth. Over 60% of the peptides in the permeate were hydrophobic, whereas 70% of the peptides in the adsorption cake were hydrophilic. Irreversible resistance was the predominant resistance during NF processing, and the fouling behaviour of hydrophilic fractions was dominant.
- Carbon footprint of water reuse and desalination: a review of greenhouse
gas emissions and estimation tools
- Authors: Pablo K. Cornejo; Mark V. E. Santana, David R. Hokanson, James R. Mihelcic Qiong Zhang
Abstract: As population and water demand increase, there is a growing need for alternative water supplies from water reuse and desalination systems. These systems are beneficial to water augmentation; however, there are concerns related to their carbon footprint. This study compiles the reported carbon footprint of these systems from existing literature, recognizes general trends of carbon footprint of water reuse and desalination, and identifies challenges associated with comparing the carbon footprint. Furthermore, limitations, challenges, knowledge gaps, and recommendations associated with carbon footprint estimation tools are presented. Reverse osmosis (RO) technologies were found to have lower CO2 emissions than thermal desalination technologies and the estimated carbon footprint of seawater RO desalination (0.4–6.7 kg CO2eq/m3) is generally larger than brackish water RO desalination (0.4–2.5 kg CO2eq/m3) and water reuse systems (0.1–2.4 kg CO2eq/m3). The large range of reported values is due to variability in location, technologies, life cycle stages, parameters considered, and estimation tools, which were identified as major challenges to making accurate comparisons. Carbon footprint estimation tools could be improved by separating emissions by unit process, direct and indirect emissions, and considering the offset potential of various resource recovery strategies.
- Review of the leading challenges in maintaining reclaimed water quality
during storage and distribution
- Authors: Patrick Jjemba; William Johnson, Zia Bukhari Mark LeChevallier
Abstract: Reclaimed water quality has largely focused on meeting standards in the treated effluent. While the focus is well placed, reclaimed water may change before it is used at dispersed locations. Reclaimed water is a perishable product with a shelf life requiring packaging (i.e., piping) and preserving (with a disinfectant) during storage to minimize deterioration in quality. It typically contains higher nutrient levels compared to potable water. Based on an online survey, the challenges were characterized into nine categories in order of importance: infrastructure, water quality, customer relations, operational, cost (pricing), capacity/supply, regulation, workforce, and miscellaneous. The first five categories accounted for 80% of the challenges raised by the industry. A review of the literature provided various remedies to these challenges which can be incorporated into best management practices for controlling potential health and aesthetic issues associated with storage and distribution of reclaimed water.