Urban wastewater treatment with mature constructed wetlands

Despite the global acceptance for the application of vertical-flow constructed wetlands (VF CWs) as sustainable and cost-efficient technology in treating various types of wastewater, including urban wastewater, continuous loading of wetlands over time can lead to performance inefficiency and generate operational problems especially when high shock loads, such as petroleum hydrocarbon spills, are subjected to the system. Contamination with petroleum hydrocarbon compounds results in changing the structure, function and ecosystem service values of wetlands, which can eventually lead to clogging of the wetland substrate and affect the life time of the system. Sound knowledge of long-term performance in mature vertical-flow constructed wetlands linked with hydrocarbon treatment processes is needed to make guided judgments about the probable effects of a given suite of impacts and revise the management plans accordingly. A study was conducted to compare the impact of different design (aggregate size) and operational (contact time, rest time and chemical oxygen demand (COD) loading) variables on the long-term and seasonal performance of vertical-flow constructed wetland filters operated in tidal flow between June 2011 and March 2016. Ten different vertical-flow wetland systems were planted with Phragmites australis (Cav.) Trin. ex Steud. (Common Reed). Approximately 130 and 975 grams of diesel fuel (equivalent to 20 and 150 grams/litre, respectively) were each poured into four wetland filters on 26/09/2013 and 26/09/2014 respectively. Overall findings showed that the mature wetland system improved the water quality except for ortho-phosphate-phosphorus (PO₄-P), which reduced less over time. Findings also indicated that the wetland filter with the highest chemical oxygen demand (COD) loading but no diesel contamination performed the best in terms of COD and biochemical oxygen demand (BOD) removal. Filters contaminated by diesel performed worse in terms of COD and BOD but considerably better regarding nitrate-nitrogen removal. The removal efficiencies dropped for those filters impacted by the diesel spills. Seasonal analysis for water quality from different wetlands showed clear seasonal outflow concentration trends (low in summer) for COD, and nitrate-nitrogen (NO₃-N) while effluent BOD showed high treatment performance in winter. No clear seasonal trend for ammonia-nitrogen (NH₄-N), PO₄-P or suspended solids (SS) was noted. Serious clogging phenomena, impacting negatively on the treatment performance and the hydraulic conductivity, were not observed. The simulation model confirms the experimental findings that notable wetland clogging restricting the operation did not occur. Moreover, results showed that small aggregate diameter, low inflow COD load, and high contact and rest time were most efficient in reducing SS accumulation within the wetland filter bed. With regard to the treatment performance of the hydrocarbon contaminants, results indicated that all wetland systems had a relatively good performance in treating petroleum hydrocarbon compounds and the evaluation showed that all the hydrocarbon components were highly degraded and their concentrations were reduced in all treated effluents of wetland filters with time. This indicates that VF CW zones provide appropriate conditions for high treatment capacity of diesel compounds spilled with urban wastewater by a combination of processes taking place in the wetland filters, thus minimizing hydrocarbon compounds within the filter.A new experimental artificial ponds system, including: ponds with wastewater; ponds with wastewater and reeds; and ponds with wastewater, reeds and aeration, was operated in parallel with the mature experimental vertical-flow constructed wetland system, for the period between July 2015 and October 2015, to compare performance, design and operation variables between the two treatment technologies in the treatment of urban wastewater. Findings showed that highest COD and SS removals were observed for wetlands in comparison to ponds. Moreover, mature wetlands were better in removing NH₄-N and PO₄-P than ponds unless the ponds were aerated. Both systems were linked with medium to high levels of BOD removal. The aerated pond system demonstrated better treatment performance in terms of NH₄-N and PO₄-P. The NO₃-N concentration increased in the aerated ponds reflecting the high oxygen availability. Due to increasing water scarcity and droughts, which are key concerns worldwide, there is considerable interest in recycling various wastewater streams, such as treated urban wastewater, for irrigation in the agricultural sector. Recycling of effluents from various wetland filters (with/without diesel contamination) was assessed for the irrigation of chilli plants (De Cayenne; Capsicum annuum (Linnaeus) Longum Group ‘De Cayenne’) grown in a greenhouse environment. Concerning chilli fruit numbers, findings showed that the highest fruit yields for all wetland filters were associated with those that received inflow wastewater with a high loading rate, reflecting the high nutrient availability in treated wastewater, which is of obvious importance for yield production. Findings also indicated that wetlands without hydrocarbon contamination, with small aggregate size, low contact time, and low inflow loading rate provided high marketable yields (expressed in economic return). In comparison, chillies irrigated by filters with hydrocarbon contamination, small aggregate size, high contact time and high loading rate also resulted in high marketable yields of chillies, which pointed out the role of high contact time and high inflow load for better diesel degradation rates. The overall outcome of this research could considerably contribute to optimization of the design and development of long-term operation variables for constructed wetland technology particularly in petroleum industry applications. Statistically validated long-term data interpretation can particularly help the wetland modelling community and wetland managers to define, with insight into long-term and seasonal factors, removal processes for individual water quality parameters to maximize wetlands treatment performance

Treatment performance assessments of different wetland mesocosms

Despite their global acceptance as a sustainable and cost-efficient technology for water pollution control including urban wastewater contaminated with hydrocarbons, treatment performance of vertical-flow constructed wetlands can be hampered by clogging of the substrate media pores of the wetland filters. This clogging usually leads to blockage of filter substrate, progressive diminution of porosity and reduction of active pore volume, permeability and substrate hydraulic conductivity subsequently leading to poor water quality production by the wetland filters. This operational problem hinders the wider application and acceptability of these systems worldwide. In this study, different laboratory-scale vertical-flow constructed wetlands filled with gravel and planted with common reed were constructed and operated between June 2011 and March 2014 to assess treatment performances and their relationship with clogging, and diesel spill treatment as a function of hydraulic and organic loading rates, media size, and contact and rest time. Furthermore, to evaluate the hydrocarbon spill, approximately 130 grams of diesel fuel was poured into each of four wetland filters. This is the equivalent of a one-off inflow concentration of 20 g/l. A range of hydraulic loading rates was applied across the systems using real urban wastewater. Analysis of total petroleum hydrocarbon concentrations of outflow waters along with other water quality parameters was carried out to monitor both clogging and treatment performance variations. Overall, all constructed wetland systems have shown relatively high removal efficiencies for the key water quality parameters regardless of filter set-up before the hydrocarbon spill and no clogging observed. The removal efficiencies dropped for those filters impacted by the diesel spill. The filter with the highest COD loading but no diesel contamination performed the best in terms of COD and BOD removal. Furthermore, filters contaminated by diesel performed worse in terms of COD and BOD, but considerably better regarding nitrate-nitrogen removal without any apparent negative impact of within bed cloggingPertaining to seasonal variability, findings show that COD, nitrate-nitrogen and ammonia-nitrogen have shown a seasonal trend with high removal in summer compared to other seasons, while BOD removal was efficient in winter compared to summer and turbidity was greatly removed in autumn compared to other seasons. However, no clear seasonal pattern of ortho-phosphate-phosphorus and SS removal were noted. Furthermore, in the hydrocarbon contamination period, all filters regardless of the pollution, design or operation had higher removal in winter than autumn for COD, BOD, ammonia-nitrogen and ortho-phosphate-phosphorus while no seasonal trend was observed for other water quality parameters.Investigation regarding treatment performance and clogging evolution revealed that none of the systems has shown any signs of clogging after about three years of operation even with high rate Filters 7 and 8. The simulation model confirms the empirical findings that considerable filter clogging restricting the operation has not occurred. However, a small aggregate diameter, a short contact time, a long resting time and a low COD inflow concentration were most beneficial in reducing SS accumulation within the wetland filters.Treatment of the hydrocarbon pollutants was also assessed, and the investigation revealed that all the hydrocarbon components treated in the wetland filters were highly degraded (>80% removal efficiency) in all contaminated filters with some even attenuated below the detection limit. The overall outcome of this research may give useful information to wetland engineers and scientists to redesign and model configuration and operation of vertical-flow systems to increase performance and sustainability by maximizing contaminants removal efficiency for pollutants found in urban wastewater and preventing clogging occurrence in the systems. Consequently, this will help in saving cost for stakeholders in terms of operation and maintenance, and allow for progressive management of the wetland systems. Moreover, it will provide beneficial judgement for petroleum and related water industries to have confidence to incorporate wetland systems in their wastewater treatment technologies with no fear of clogging, particularly for control of hydrocarbon spills that may be released in sewage discharged to the municipal treatment plants and can also be discharged with industrial wastewater

Experimental assessment of recycled diesel spill-contaminated domestic wastewater treated by reed beds for irrigation of sweet peppers

The aim of this experimental study is to assess if urban wastewater treated by ten different greenhouse-based sustainable wetland systems can be recycled to irrigate Capsicum annuum L. (Sweet Pepper; California Wonder) commercially grown either in compost or sand within a laboratory environment. The design variables were aggregate diameter, contact time, resting time and chemical oxygen demand. The key objectives were to assess: (i) the suitability of different treated (recycled) wastewaters for irrigation; (ii) response of peppers in terms of growth when using recycled wastewater subject to different growth media and hydrocarbon contamination; and (iii) the economic viability of different experimental set-ups in terms of marketable yield. Ortho-phosphate-phosphorus, ammonia-nitrogen, potassium and manganese concentrations in the irrigation water considerably exceeded the corresponding water quality thresholds. A high yield in terms of economic return (marketable yield expressed in monetary value) was linked to raw wastewater and an organic growth medium, while the plants grown in organic medium and wetlands of large aggregate size, high contact and resting times, diesel-spill contamination and low inflow loading rate produced the best fruits in terms of their dimensions and fresh weights, indicating the role of diesel in reducing too high nitrogen concentrations

Phytoremediation of Water and Soils Contaminated by Petroleum Hydrocarbons

Resumen Durante décadas, la producción, transporte, almacenamiento y comercialización de hidrocarburos del petróleo y sus derivados, han dado origen a una problemática ambiental debida a los grandes vertimientos de combustibles que se generan. El potencial contaminante y la compleja composición de los hidrocarburos, además de su facilidad de movilización en el medio y acumulación en el agua o suelo, ha incrementado el interés científico para encontrar soluciones que reduzcan el efecto de estos compuestos en los ecosistemas. Ante esta situación, se ha evaluado la fitorremediación como una solución que por su costo-efectividad y aporte paisajístico pueden ser usados para biorremediar aguas y suelos mezclados con combustibles, minimizando el riesgo de contaminación. El presente artículo de revisión resume los principios relacionados con la fitorremediación de suelos y aguas contaminadas con hidrocarburos como una alternativa ecotecnológica que puede ser aplicada mediante la interacción de microorganismos, plantas y procesos físicos, químicos y biológicos que ocurren en los sistemas naturales como los humedales. También se discuten algunas experiencias en la temática, los factores que inciden y los mecanismos que dominan la remoción de estos compuestos orgánicos. Abstract The production, transport, storage, and commercialization of petroleum hydrocarbons with their derivatives have become an environmental problem as a result of the large fuel spills frequently generated over the years. The contaminating potential and the complex composition of hydrocarbons and its derivates,on top of their easiness of mobilization in the environment and their accumulation in water and soils, have increase the scientific interest in orderto find a solution to reduce their effect on the ecosystems. Therefore, researchers worldwide have focused on evaluating phytoremediation as a solution in view of its cost-effectiveness and landscaping contribution because it can be used to bioremediatewater and soils mixed with fuels, minimizing the risk of pollution. This review article summarizes the principles related to phytoremediation of soils and water contaminated with hydrocarbons as an ecotechnological alternative that can be applied through the interactions between microorganism, plants and physical, chemical and biological processes that occur in natural systems like the wetlands. This paper also discusses some experiences about the subject, factors related and removal mechanisms that command the removal of the organic compounds

Recycling of domestic wastewater treated byvertical-flow wetlands for irrigating crops

Due to water scarcity in many semi-arid countries, there is considerable interest in recycling various nutrient-rich wastewater streams, such as treated urban wastewater, for irrigation in the agricultural sector. The aim is therefore to assess if domestic wastewater treated by different sustainable wetland systems (some contaminated by diesel spills) can be successfully recycled to irrigate commercially grown crops such as Sweet Pepper (California Wonder; cultivar of Capsicum annuum Linnaeus Grossum Group) and Chilli (De Cayenne; Capsicum annuum (Linnaeus) Longum Group 'De Cayenne') grown either in compost or sand within a laboratory environment. The objectives were to assess the suitability of the irrigation water for long-term growth when using recycled wastewater, the impact of different treated wastewaters as a function of the wetland type, the impact of treated wastewater volume for irrigation, the suitability of different growth media for vegetable growth irrigated with treated wastewater, the effect of a diesel oil spill on the suitability of the recycled wastewater for vegetable irrigation, the economic return of various experimental systems in terms of marketable yields, the impact of differently treated wastewater on soil and fruit mineral and microbial contamination as a function of the wetland type as well as its operation and management, and the possibility of regenerating Capsicum annuum using the mother plant’s seed and irrigation with recycled wastewater treated by constructed wetlands to obtain a new cultivar adapted to urban wastewater. Vertical-flow constructed wetlands treated the domestic wastewater well, meeting the irrigation water quality standards for most water quality parameters with exception of phosphorus, ammonia-nitrogen, potassium and total coliforms, which showed high values significantly (p < 0.05) exceeding the thresholds set for irrigation purposes. The growth of both Sweet Pepper and Chilli fed with different treated and untreated wastewater types was assessed. A few plants suffered from either a shortage and/or excess of some nutrients and trace minerals. The overall growth development of Sweet Peppers was poor due to the high concentrations of nutrients and trace minerals. However, a high Sweet Peppers yield in terms of economic return (marketable yield expressed in monetary value) was linked to raw wastewater and an organic growth medium, while the plants grown in organic medium and irrigated with outflow from wetlands of large aggregate size, high contact and resting times, diesel-spill contamination and low inflow loading rate produced the best fruits in terms of their dimensions and fresh weights, indicating the role of diesel in reducing too-high nitrogen concentrations. In contrast, Chillies did reasonably well but the growth of foliage was excessive and the harvest was delayed. High Chilli yields in terms of economic return were associated with tap water and an organic growth medium, and a wetland with a small aggregate size and short contact time and long resting time with a low inflow loading rate, while the best fruit quality in terms of length, width and weight was observed for plants grown in organic media and irrigated with outflow water from wetlands containing small aggregates with long contact and resting times and fed with a high inflow loading rate (undiluted wastewater), releasing more nutrients into their effluent resulting in a greater marketable profit. Low fruit numbers correlated well with inorganic growth media. Filters contaminated with hydrocarbon were usually associated with a substantially lower Chilli marketable yield than those filters lacking hydrocarbon pollution. Chilli generations were grown successfully when using wastewater treated by constructed wetlands and organic soil. High Chilli generation yields in terms of economic return were associated with wetlands containing small aggregates with long contact and resting times and fed with a high inflow loading rate (undiluted wastewater), releasing more nutrients into their effluent producing the best fruit quality in terms of length, width and weight resulting in a greater marketable profit. Chilli generation plants were grown with considerably shorter heights and produced abundant fruit numbers which were harvested earlier than their mothers due to the reduction of irrigation water volume applied on them compared to their mothers. However, excessive nutrients applied on mother plants via irrigation water resulted in better fruit quality in terms of dimensions and weights compared with their generations, leading to a greater marketable profit. Findings indicate that nutrient concentrations supplied to the crops by a combination of compost and treated wastewater are usually too high to produce a good harvest. However, as the compost was depleted of nutrients after about ten months, the harvest increased for pots that received pre-treated wastewater. The productivity of crops in terms of harvest was independent of the wastewater consumption volume, but may have depended on the water quality. A high yield was related to the most suitable provision of nutrients and trace elements. The mineral content of the organic soil was significantly higher than that for the inorganic soil, before and after irrigation with treated wastewater. No substantial mineral contamination was observed in the soils due to irrigation with treated wastewater. Slight to moderate zinc contamination was detected in harvested fruits based on common standards for vegetables. No bacterial contamination was detected for fruits harvested from plants irrigated with wetland outflow water. In contrast, fruits harvested from those plants irrigated with preliminary treated wastewater showed high contamination by total coliforms, Streptococcus spp. and Salmonella spp., especially for fruits which were located close to the contaminated soil surface. However, findings indicate that vegetables receiving wastewater treated with wetlands can be considered as safe compared to those receiving only preliminarily treated wastewater. The project contributes to ecological sanitation understanding by closing the loop in the food and water chain. Findings will lead to a better understanding of the effects of different wetland treatment processes on the recycling potential of their outflow waters

Crude Oil

Petroleum crude oil is the main energy source worldwide. However, global fossil fuel resources and reservoirs are rapidly and disturbingly being depleted. Thus, it is particularly important to shed light on new techniques developed for economic production and better utilization of crude oil. In addition, the processes involved in the production, refining, and transportation of crude oil are environmentally hazardous. It is essential to develop cleaner technologies and to find innovative solutions to overcome these problems. Over four sections, this book discusses materials used in cracking crude oil and improving its specifications, methods for reducing or eliminating the hazardous effects of petroleum pollution, and the environmental effects of crude oil, as well as presents case studies from different countries

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