Impact of climate change on wetland ecosystems: A critical review of experimental wetlands.

Climate change is identified as a major threat to wetlands. Altered hydrology and rising temperature can change the biogeochemistry and function of a wetland to the degree that some important services might be turned into disservices. This means that they will, for example, no longer provide a water purification service and adversely they may start to decompose and release nutrients to the surface water. Moreover, a higher rate of decomposition than primary production (photosynthesis) may lead to a shift of their function from being a sink of carbon to a source. This review paper assesses the potential response of natural wetlands (peatlands) and constructed wetlands to climate change in terms of gas emission and nutrients release. In addition, the impact of key climatic factors such as temperature and water availability on wetlands has been reviewed. The authors identified the methodological gaps and weaknesses in the literature and then introduced a new framework for conducting a comprehensive mesocosm experiment to address the existing gaps in literature to support future climate change research on wetland ecosystems. In the future, higher temperatures resulting in drought might shift the role of both constructed wetland and peatland from a sink to a source of carbon. However, higher temperatures accompanied by more precipitation can promote photosynthesis to a degree that might exceed the respiration and maintain the carbon sink role of the wetland. There might be a critical water level at which the wetland can preserve most of its services. In order to find that level, a study of the key factors of climate change and their interactions using an appropriate experimental method is necessary. Some contradictory results of past experiments can be associated with different methodologies, designs, time periods, climates, and natural variability. Hence a long-term simulation of climate change for wetlands according to the proposed framework is recommended. This framework provides relatively more accurate and realistic simulations, valid comparative results, comprehensive understanding and supports coordination between researchers. This can help to find a sustainable management strategy for wetlands to be resilient to climate change.

Highlights of the novel dewaterability estimation test (DET) device.

Many industries, which are producing sludge in large quantities, depend on sludge dewatering technology to reduce the corresponding water content. A key design parameter for dewatering equipment is the capillary suction time (CST) test, which has, however, several scientific flaws, despite that the test is practical and easy-to-perform. The standard CST test has a few considerable drawbacks: its lack of reliability and difficulties in obtaining results for heavy sludge types. Furthermore, it is not designed for long experiments (e.g. >30 min), and has only two measurement points (its two electrodes). In comparison, the novel dewaterability estimation test (DET) test is almost as simple as the CST, but considerably more reliable, faster, flexible and informative in terms of the wealth of visual measurement data collected with modern image analysis software. The standard deviations associated with repeated measurements for the same sludge is lower for the DET than for the CST test. In contrast to the CST device, capillary suction in the DET test is linear and not radial, allowing for a straightforward interpretation of findings. The new DET device may replace the CST test in the sludge-producing industries in the future.

Phytoremediation performance of floating treatment wetlands with pelletized mine water sludge for synthetic greywater treatment.

PURPOSE: Buckets containing floating reed (Phragmites australis) simulated floating treatment wetlands (FTWs) and were used to improve the remediation performance of synthetic greywater (SGW). The aim of the study was to investigate the behaviour of FTWs for treatment of key contaminants within artificial greywater. METHODS: Pelletized ochre based on acid mine water sludge was introduced to selected FTWs, because of its capability in sequestration phosphorus and other trace elements. The impact of the following four operational variables were tested in the experimental set-ups of the FTWs (four replicates each): pollutant strength (high- (HC) and low- (LC) concentrations), treatment time (2- or 7-days of hydraulic retention time (HRT)), presence or absence of macrophytes (P. australis) and cement-ochre pellets. RESULTS: The results showed that 5 - day biochemical oxygen demand (BOD) and chemical oxygen demands (COD) were significantly (p < 0.05) reduced in all wetlands. Nitrate-nitrogen (NO3-N) concentrations were significantly (p < 0.05) higher, and those measurements for PO4-P were significantly (p < 0.05) lower than the corresponding ones determined for the influent. The existence of ochre pellets with P. australis significantly (p < 0.05) decreased B, Cd, Cr, Cu, Mg, Ni and Zn concentrations, but increased Al, Ca, Fe and K concentrations in the effluent, with the exception of sodium (Na). CONCLUSIONS: The FTW performances can be improved by utilising ochre-cement pellets to increase the pH of greywater. The presence of P. australis acts as a buffer to neutralise the pH of SGW. Rhizomes and biofilms mitigate increases in turbidity, TSS and colour values.

Contaminations of Soil and Two Capsicum annuum Generations Irrigated by Reused Urban Wastewater Treated by Different Reed Beds.

Background: In order to save potable water, this study aims to evaluate the contamination of soil and Capsicum annuum L. (chilli) watered with urban wastewater (sewage) pre-treated by various wetland systems. Methods: The appropriateness of wetland outflow for irrigation when applying reused wastewater with high contamination of minerals and pathogens was assessed. The impact of wastewaters pre-treated by various wetlands on soil and harvest was tested in terms of mineral and biological contamination risk. Results: The wetlands met the standards for irrigation water for most water quality variables. However, the thresholds for key water quality parameters were significantly (p < 0.05) exceeded. The highest values for total coliforms, ammonium-nitrogen, phosphorus and potassium were 157,072 CFU/100 mL, 8.5 mg/L, 5.0 mg/L, and 7.0 mg/L, respectively. The harvest was moderately polluted only by zinc according to vegetable quality standards (threshold of 50 mg/kg). Zinc concentrations for Filters 2, 4, 6, 7 and 8 were 35.8, 60.6, 65.1, 65.5 and 53.2 mg/kg, respectively. No bacterial contamination was detected. Conclusions: Treatment of domestic wastewater applying constructed wetlands and subsequent recycling of the treated wastewater for irrigation of crops is a good substitute to the traditional application of drinking water for irrigation purposes.

Wetlands for wastewater treatment and subsequent recycling of treated effluent: a review.

Due to water scarcity challenges around the world, it is essential to think about non-conventional water resources to address the increased demand in clean freshwater. Environmental and public health problems may result from insufficient provision of sanitation and wastewater disposal facilities. Because of this, wastewater treatment and recycling methods will be vital to provide sufficient freshwater in the coming decades, since water resources are limited and more than 70% of water are consumed for irrigation purposes. Therefore, the application of treated wastewater for agricultural irrigation has much potential, especially when incorporating the reuse of nutrients like nitrogen and phosphorous, which are essential for plant production. Among the current treatment technologies applied in urban wastewater reuse for irrigation, wetlands were concluded to be the one of the most suitable ones in terms of pollutant removal and have advantages due to both low maintenance costs and required energy. Wetland behavior and efficiency concerning wastewater treatment is mainly linked to macrophyte composition, substrate, hydrology, surface loading rate, influent feeding mode, microorganism availability, and temperature. Constructed wetlands are very effective in removing organics and suspended solids, whereas the removal of nitrogen is relatively low, but could be improved by using a combination of various types of constructed wetlands meeting the irrigation reuse standards. The removal of phosphorus is usually low, unless special media with high sorption capacity are used. Pathogen removal from wetland effluent to meet irrigation reuse standards is a challenge unless supplementary lagoons or hybrid wetland systems are used.

Treatment of contaminated greywater using pelletised mine water sludge.

Precipitated sludge (ochre) obtained from a mine water treatment plant was considered as an adsorbent substance for pollutants, since ochre is relatively free from problematic levels of toxic elements, which could impair on the quality of water to be treated. Artificially created ochre pellets from mixing Portland cement with raw ochre sludge were utilised to remediate either high (HC) or low (LC) contaminated synthetic greywater (SGW) in mesocosm-scale stabilisation ponds at 2-day and 7-day contact times under real weather conditions in Salford. After a specific retention time, treated SGW was agitated before sampling to evaluate pollutant removal mechanisms (other than sedimentation) such as adsorption by ochre pellets, before replacing the treated water with new inflow SGW. The results showed that cement-ochre pellets have a high ability to adsorb ortho-phosphate-phosphorous (PO4-P) significantly (p < 0.05) by 70.7% and 56.0% at 7-day contact time for HC-SGW and LC-SGW, respectively. After the experiment, an analysis revealed that elements such as boron (B), cadmium (Cd), magnesium (Mg), manganese (Mn), nickel (Ni) and zinc (Zn) accumulated significantly (p < 0.05) within the ochre pellets. The notable accumulation of Cd within ochre pellets reflects the significant (p < 0.05) remediation of greywater during the first 35 and 20 successive times of treatment for HC-SGW at 2- and 7-day contact times, respectively. Cadmium was still adsorbed significantly (p < 0.05) during the treatment of LC-SGW. However, the calcium (Ca) content decreased significantly (p < 0.05) within ochre pellets treating both types of greywaters due to mobilisation. The corresponding increases of Ca in greywater were significant (p < 0.05).

Monitoring and assessment of treated river, rain, gully pot and grey waters for irrigation of Capsicum annuum.

This study examines the benefits and risks associated with various types of wastewater recycled for vegetable garden irrigation and proposes the best water source in terms of its water quality impact on crop yields. The aim was to evaluate the usability of river, rain, gully pot, real grey and artificial grey waters to water crops. The objectives were to evaluate variables and boundary conditions influencing the growth of chillies (De Cayenne; Capsicum annuum (Linnaeus) Longum Group 'De Cayenne') both in the laboratory and in the greenhouse. A few irrigated chilli plants suffered from excess of some nutrients, which led to a relatively poor harvest. High levels of trace minerals and heavy metals were detected in river water, gully pot effluent and greywater. However, no significant differences in plant yields were observed, if compared with standards and other yields worldwide. The highest yields were associated with river water both in the laboratory and in the greenhouse. Plant productivity was unaffected by water quality due to the high manganese, potassium, cadmium and copper levels of the greywater. These results indicate the potential of river water and gully pot effluent as viable alternatives to potable water for irrigation in agriculture.

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.