Constructed wetland for sustainable and low-cost wastewater treatment: review article

There is a growing need for more sustainable wastewater treatment technologies to provide non-conventional water sources. Constructed Wetland systems (CW) are viewed as a low-cost treatment technology with proven treatment efficiency. CWS can treat a variety of contaminants using low energy and natural systems by altering various design parameters. There are two configuration types of constructed wetlands: vertical (VF) and horizontal flow CW (HF). Both configurations have been widely adopted in both large and pilot scale studies with proven records of reasonable wastewater treatment efficiency. The current article reviews the recent development of CW technology and highlights the main achievements and successful applications for wastewater treatment at various locations. The review has indicated that a considerable removal efficiency is attained while using engineered CW systems with variable treatment rates for various pollutants. The treatment efficiency is a function of various parameters including wastewater type, scale dimensions, applied plant and the retention time. The review compared the treatment efficiency for both VF and HF and has revealed that various removal rates of BOD, COD, TSS, TN, TP and NH₄ was attained using both configurations. Yet, the removal efficiency in the case of VF was slightly higher compared with the HF with an average treatment level of 77% and 68% was achieved in both systems, respectively. The review revealed that the CW is an effective and sustainable technology for wastewater treatment with the initial influent level, microbial biofilm, detention time, plant species and configuration among the most dominating parameters that are directly controlling the removal rates

Treatment of petroleum refinery wastewater with constructed wetlands

The use of constructed wetlands (CWs) for polishing of petroleum refinery wastewater in Nigeria was evaluated. Secondary treated petroleum refinery wastewater from a refinery (Kaduna, Nigeria) was characterized with different types of organic and inorganic pollutants (Chapter 3). Vertical subsurface flow (VSSF) CWs planted with locally available macrophytes (Cyperus alternifolius and Cynodon dactylon) were designed and built for polishing of secondary treated refinery wastewater in terms of organic matter, nutrients and suspended solids removal (Chapter 4). The tertiary treated refinery wastewater did, however, not meet effluent discharged compliance limits in terms of total suspended solids (TSS), biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and ammonium-N (NH4+-N) removal. Typha latifolia planted-VSSF CWs could, however, treat TSS, BOD5, COD and NH4+-N in the petroleum refinery wastewater to below World Health Organization and Federal Environmental Protection Agency (Nigeria) effluent discharge limits of 30 mg/L for TSS, 10 mg/L for BOD5, 40 mg/L for COD and 0.2 mg/L for NH4+-N (Chapter 5). T. latifolia-planted VSSF CW achieved higher removal efficiencies for all parameters measured in comparison to C. alternifolius and C. dactylon planted-VSSF CWs. In addition, the T. latifolia-planted VSSF CW had the best heavy metal removal performance, followed by the C. alternifolius-planted VSSF CW and then the C. dactylon-planted VSSF CW (Chapter 6). The accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09 - 16 %) of the overall heavy metal removal by the wetlands. Coupling a horizontal subsurface flow (HSSF) CW to the VSSF CW (hybrid CW) further improved effluent quality with an overall BOD5 and PO43--P removal efficiency of, respectively, 94% and 78% (Chapter 5). Diesel contaminated wastewater was treated in the hybrid CWs spiked with three different nutrient concentrations. Numerical experiments were performed to investigate the biodegradation of the diesel compounds in the synthetic contaminated wastewater by the duplex-CWs using constructed wetland 2D. The VF CWs had a higher removal efficiency than the HFF CWs and the hybrid CW showed higher removal efficiencies in the days with nutrient application than the days without nutrient application (Chapter 8). This study showed that VSSF CWs planted with T. latifolia, C. alternifolius and C. dactylon can be used for the removal of suspended solids, organic contaminants and heavy metals from secondary refinery wastewater under tropical climate conditions. Especially T. latifolia-planted hybrid CWs are viable alternatives for the treatment of secondary refinery wastewater to below standards of the World Health Organization and Federal Environmental Protection Agency (Nigeria) under the prevailing climatic conditions in Nigeria.</p

Optimization of continuous vermifiltration processes for small communities

Esta tese foca-se no estudo da optimização de um processo descentralizado de vermifiltração para tratamento de água residual urbana. O processo é avaliado tanto sob o ponto de vista técnico e ambiental numa perspectiva de sustentabilidade, no qual se incluem a optimização de um sistema de vermifiltração em pequena-escala, complementado com estudos de análise de ciclo de vida. As tecnologias de tratamento de água residual incluem sistemas centralizados, mais comuns em zonas urbanas, e sistemas descentralizados, mais comuns em aglomerados populacionais dispersos e pequenas comunidades rurais. Os sistemas descentralizados têm vindo progressivamente a ser considerados como soluções mais sustentáveis. Muitos não requerem fornecimento de electricidade, operação dispendiosa ou sofisticada, sendo de fácil adaptação em diferentes contextos geográficos. Os sistemas secos controlados são aconselhados para regiões áridas e aglomerados dispersos sem sistemas centralizados de saneamento. Dado que diversas tecnologias descentralizadas secas e húmidas poderão ser importantes fontes de contaminação, encontram-se em aberto diversas oportunidades para investigação, incluindo, não apenas a conversão de sistemas rudimentares em sistemas controlados nas tecnologias secas, como também a inclusão de sistemas de tratamento secundário como completamento aos sistemas de tratamento primário nas tecnologias húmidas. A vermifiltração combina filtração com vermicompostagem, tratando-se de uma tecnologia sustentável e de baixo custo que apresenta elevadas eficiências de tratamento, mesmo quando sujeita a reduzidos caudais de água residual. Tem sido aplicada com sucesso em habitações, pequenas ETAR, tanto para águas residuais urbanas como industriais. Numa primeira fase, procedeu-se à optimização do sistema de vermifiltração. O procedimento envolveu a identificação das melhores variáveis hidráulicas, densidade de minhocas, e configuração do sistema, na avaliação de um sistema unitário e um sistema sequencial. As eficiências óptimas de tratamento foram obtidas para um tempo de retenção hidráulico de 6 horas, um caudal hidráulico de 0.89 m3 m-2 dia-1, e 177.6 g CBO m-2 dia-1 de taxa de carga orgânica. As melhores eficiências foram obtidas para uma densidade de minhocas de 20 g L-1 tendo sido atingidos valores para CBO5, CQO, SST e NH4+ de 97.5%, 74.3%, 98.2% e 88.1%, respectivamente. O sistema sequencial permitiu o aumento significativo das eficiências de tratamento quando comparado com o sistema unitário, tendo-se obtido eficiências de tratamento de 98.5% for CBO5, 74.3% for tCOD, 96.6% for TSS, and 99.1% for and NH4+. Posteriormente, de modo a avaliar o meio de enchimento mais adequado, duas alternativas foram testadas, especificamente vermicomposto e serradura. As eficiências de tratamento foram de 91.3% para CBO5, 87.6% para CQO, 98.4% para SST, e 76.5% para NH4+ em VE, e 90.5% para CBO5, 79.7% para CQO, 98.4% para SST, e 63.4% para NH4+ em SE. As minhocas contribuíram para reduzir as remoções de NH4+ e Azoto Total, e para aumentar a concentração de NO3- no efluente tratado. Comparativamente à água residual bruta, o vermicomposto contribuiu para aumentar a concentração de Fósforo Total. Em todos os tratamentos, as eficiências foram ainda insuficientes para cumprir a regulamentação da EU para descargas de água residual em meios aquáticos sensíveis (Azoto e Fósforo Totais) e as orientações da USEPA e OMS para irrigação (coliformes fecais). Ainda assim, todos os tratamentos removeram ovos de helmintes. Desenvolveu-se uma análise de ciclo de vida por forma a comparar os sistemas de vermifiltração com outras tecnologias alternativas. Este procedimento incluiu um sistema de filtração lenta, um leito de macrófitas e um sistema de lamas activadas. O inventário de ciclo de vida permitiu identificar que os recursos materiais foram mais usados durante a fase de construção comparativamente a qualquer outra fase. Dadas as pequenas populações servidas, a quantidade de materiais usados por habitante foi mais elevada relativamente às quantidades encontradas para outras infraestruturas de maior dimensão. A electricidade foi o recurso mais utilizado durante a fase de operação, tendo sido um resultado expectável. Quando comparada com os leitos de macrófitas, a vermifiltração permitiu obter importantes benefícios ambientais na maioria das categorias de impacte, em particular durante a fase de construção. Comparativamente à filtração lenta, a vermifiltração originou a melhoria das categorias de impacte acidificação e eutrofização, ao mesmo tempo que originou a deterioração das restantes. A vermifiltração pode apresentar-se como uma melhor solução sob o ponto de vista ambiental que os sistemas de leitos de macrófitas e lamas activadas, fruto dos melhores resultados obtidos na maioria das categorias de impacte. Em todas as soluções de tratamento os impactes durante a fase de construção ultrapassaram os impactes das restantes fases, devido ao pequeno número de habitantes servidos, não atingindo economias de escala. Durante a elaboração desta tese, diversas questões ficaram por responder, nomeadamente: i) o impacte das variáveis climáticas na dinâmica do tratamento e das eficiências, e que afectam o rendimento e a resiliência do processo segundo diferentes inputs de carga orgânica e temperaturas; qual o tipo de meio de enchimento mais adequado para o processo, em particular o que melhor contribui para a economia circular; e iii) a aplicabilidade, tanto do ponto de vista técnico como legal, do vermicomposto no solo, como fertilizante, aquando e futuras análises de ciclo de vida, deve ser incluída nas fronteiras do sistema.This study was fully supported by the Portuguese company FUTURAMB®

Performance evaluation and cost analysis of subsurface flow constructed wetlands designed for ammonium-nitrogen removal

Subsurface flow constructed wetlands (SSF CWs) is a low-cost, environmentally friendly sanitation technology for on-site treatment of domestic/municipal sewage. However, these systems are apparently unable to produce treated water of a quality suitable for discharge particularly in terms of nitrogen concentration, which has been attributed to design and operation based on biological oxygen demand as the parameter of choice. The aim of this study was to evaluate the performance, support medium, and techno-economics of a vertical- horizontal (V-H) SSF hybrid CW designed and operated using ammonium-nitrogen (NH4+-N) as the major parameter. Two pilot scale V-H SSF hybrid CWs were designed, constructed, and the performance of each monitored over two seasons and under two phases i.e. an initiation phase, and an optimization phase. Laboratory-scale horizontal SSF CWs were used to evaluate the support medium while the techno-economic study was framed to determine the cost effectiveness of V-H SSF hybrid CWs relative to high rate algal oxidation pond (HRAOP) systems to increase capacity of overloaded and/or under-performing waste stabilization pond (WSP) sewage treatment plants. Results revealed that under optimal operating conditions of hydraulic loading rate, hydraulic retention, and influent NH4+-N loading rate, treated water from the V-H SSF hybrid CWs achieved a quality commensurate with current South African standards for discharge into a surface water resource for all parameters except chemical oxygen demand and faecal coliforms. This suggests that NH4+-N is an important design and operational parameter for SSF CWs treating municipal sewage that is characterised as weak in terms of NH4+-N with a requirement of only simple disinfection such as chlorination to eliminate faecal coliforms. Use of discard coal to replace gravel as support medium in horizontal SSF CWs revealed an overall reduction in elemental composition of the discard coal support medium but without compromising water quality. This result strongly supports use of discard coal as an appropriate substrate for SSF CWs to achieve acceptable water quality. Furthermore, simultaneous degradation of discard coal during wastewater treatment demonstrates the versatility of SSF CWs for use in bio-remediation and pollution control. Finally, a technoeconomic assessment of V-H SSF hybrid CWs and a HRAOP series was carried out to determine the suitability of each process to increase capacity by mitigating dysfunctional and/or overloaded WSP sewage treatment plants. Analysis revealed that the quality of treated water from both systems was within the South African General Authorization standards for discharge to a surface water resource. Even so, each technology system presented its own set of limitations including; the inability to satisfactorily remove NH4+-N and chemical oxygen demand (i.e. for V-H SSF hybrid CWs) and total suspended solids and faecal coliforms (i.e. for HRAOPs), and a requirement for substantial land footprint while, HRAOPs required significantly less capital than V-H SSF hybrid CWs for implementation. The latter suggests that HRAOPs could be preferred over V-H SSF hybrid CWs as a technology of choice to increase the capacity of overloaded WSP sewage treatment plants especially where financial resources are limited. Overall, the results of this thesis indicate the potential to use NH4+-N as a design parameter in constructing SSF CWs treating weak strength municipal sewage (i.e. in terms of NH4+-N concentration) and to supplant gravel as the treatment media with industrial waste material like discard coal to achieve wastewater treatment, bio-remediation, and pollution control. The results of this work are discussed in terms of using SSF CWs as a passive and resilient technology for the treatment of domestic sewage in sub-Saharan Africa

Financial viability of sustainable infrastructural development at the Nelson Mandela Metropolitan University

Sustainable environmental practices need to be integrated into a university's infrastructural operations. Universities are entities that function within financial constraints with varying priorities across both administrative and educational functions. Unfortunately, these financial constraints often imply that a university's potential leadership role can only be realised should the viability (business case) of a proposed intervention be determined. This study focuses on the determination of a relational sustainable indicator and a relational cost factor. A relational sustainable indicator demonstrates how a university can collectively determine the contribution made to sustainability by various sectors of infrastructure. This is developed by means of a secondary study. Two components are important for calculating the relational sustainability indicator, namely, green infrastructure attributes and the basic elements of sustainability systems, namely, the environmental, economic and social dimensions of sustainability. The determination of a relational cost factor involves the quantification of the costs associated with alternative infrastructure provision. In particular, attention is paid to demand-side management costs, rationalising spatial growth costs, green building development costs, operation and maintenance of existing buildings costs, wastewater infrastructure costs, water infrastructure costs, energy infrastructure costs and transport infrastructure costs. Once the actual costs of each intervention category are determined, a relational sustainable cost factor can be calculated. Utilising the costs in the eight categories identified, a relational sustainable cost factor is determined. A resultant relational cost benefit as per the eight defined categories of sustainable infrastructure provision is derived from the relevant costs of sustainable infrastructure provision, the resultant relational cost factors and, finally, the relational sustainability indicators. It is proposed that that the determination of a budget split between the various interventions based on the resultant relational cost factor occur as follows: - Demand side management interventions: 15.97percent - Rationalising spatial growth: 6.72percent - Construction of green buildings: 24.37percent - Operations and maintenance: 21.85percent - Wastewater: 7.56percent - Water: 1.68percent - Energy: 12.61percent - Transport: 9.24percent. This study provides a platform to guide how and where to invest in sustainable infrastructure and provide direction in determining a budget split between various categories of sustainable infrastructure development