A Review on Constructed Treatment Wetlands for Removal of Pollutants in the Agricultural Runoff

Constructed wetland (CW) is a popular sustainable best management practice for treating different wastewaters. While there are many articles on the removal of pollutants from different wastewaters, a comprehensive and critical review on the removal of pollutants other than nutrients that occur in agricultural field runoff and wastewater from animal facilities, including pesticides, insecticides, veterinary medicine, and antimicrobial-resistant genes are currently unavailable. Consequently, this paper summarized recent findings on the occurrence of such pollutants in the agricultural runoff water, their removal by different wetlands (surface flow, subsurface horizontal flow, subsurface vertical flow, and hybrid), and removal mechanisms, and analyzed the factors that affect the removal. The information is then used to highlight the current research gaps and needs for resilient and sustainable treatment systems. Factors, including contaminant property, aeration, type, and design of CWs, hydraulic parameters, substrate medium, and vegetation, impact the removal performance of the CWs. Hydraulic loading of 10–30 cm/d and hydraulic retention of 6–8 days were found to be optimal for the removal of agricultural pollutants from wetlands. The pollutants in agricultural wastewater, excluding nutrients and sediment, and their treatment utilizing different nature-based solutions, such as wetlands, are understudied, implying the need for more of such studies. This study reinforced the notion that wetlands are effective for treating agricultural wastewater (removal >90%) but several research questions remain unanswered. More long-term research in the actual field utilizing environmentally relevant concentrations to seek actual impacts of weather, plants, substrates, hydrology, and other design parameters, such as aeration and layout of wetland cells on the removal of pollutants, are needed.

Strategies of Utilising Agriculture Wastewater for Microalgae Cultivation and Its Possible Applications: A Review

Microalgae have been found to have high prospects in wastewater treatment, particularly from agriculture. However, the uneconomical algal medium growth has become the major disadvantaged in algal industry. Multiple attempts includes the development of microalgae phycoremediation technology has been integrated into wastewater treatment to reduce the cost of expensive wastewater remediation. Utilising wastewater as a low-cost nutrient medium offers a synergistic effect of wastewater nutrient removal and co-production of valuable biomass simultaneously. This paper is mainly focused on potential, ability, strategy, application (i.e., palm oil wastewater), limitation and challenges of microalgae in agricultural wastewater treatment using phycoremediation. The understanding of cultivating microalgae using agriculture wastewater shall promote the utilisation of wastewater more sustainably in the future. The possible solutions in the application of microalgae for aquaculture and agriculture sector is also discussed in this review. Overall, the utilisation of wastewater in media cultivation for microalgae is restricted due to the expensive treatment and safety concern. However, this pitfall can be reduced in the future together with a further intensive scientific study, advanced technology, better management system and applying better standard protocol.

Assessment of Nutrient Usage and Discharge in Tomato Greenhouse

One of the contributors to eutrophication is from agricultural wastewater which contained nutrients such as nitrogen and phosphorus. The agricultural industry in Japan has practice greenhouse plantation recently. In this study, the amount of nutrient concentration and load in the wastewater were investigated. Water samples from water supply, soil medium and effluent were collected at a greenhouse in Japan which cultivated tomato plants in coconut husk medium. The assessment was conducted every two weeks for regular monitoring for three months. The results showed that concentrations of all nutrients have same concentration level in the water supply samples from January 13th to March 15th. The concentration of supplied nutrient on March 29th increased due to high concentration of nutrients in medium water samples which preventing the nutrient uptake by the plant. The nutrient uptake by the plants were in the same range which NH4-N was between 13.6 mg/L to 14.99 mg/L, NO2-N was between 2.3 to 2.5 mg/L, NO3-N was between 135.9 mg/L to 152.5 mg/L and PO4-P was between 70.12 to 76.64 mg/L. The concentration of nutrients in drainage was below the permissible limit of Japan’s Effluent Standard. As a result, it can be concluded that using greenhouses as an alternative farming method contributes in reducing nutrient discharge by controlling the nutrient supply to the plants.

Fluometuron Removal from Agricultural Wastewater in Porous Media Filters

In the present study, six gravity filters were constructed and evaluated for the treatment of agricultural wastewater contaminated with herbicide fluometuron. Two filter types in terms of feeding strategy (i.e., batch and continuous feeding strategies), three porous media (i.e., coarse gravel, coarse zeolite and fine zeolite) and three hydraulic residence times (i.e., 1 day, 2 days and 4 days) were evaluated to find the best design and operation parameter in fluometuron removal by adsorption on porous media. Batch experiments were also conducted and the experimental data were fitted to adsorption kinetic and isotherm models. Results showed that the experimental data fitted better to the pseudo-first order model and to the Freundlich model, and the highest fluometuron adsorption was recorded for fine zeolite. The results of filter operation indicated that the most important parameter affecting fluometuron removal is the hydraulic residence time.

Diffuse Water Pollution from Agriculture: A Review of Nature-Based Solutions for Nitrogen Removal and Recovery

The implementation of nature-based solutions (NBSs) can be a suitable and sustainable approach to coping with environmental issues related to diffuse water pollution from agriculture. NBSs exploit natural mitigation processes that can promote the removal of different contaminants from agricultural wastewater, and they can also enable the recovery of otherwise lost resources (i.e., nutrients). Among these, nitrogen impacts different ecosystems, resulting in serious environmental and human health issues. Recent research activities have investigated the capability of NBS to remove nitrogen from polluted water. However, the regulating mechanisms for nitrogen removal can be complex, since a wide range of decontamination pathways, such as plant uptake, microbial degradation, substrate adsorption and filtration, precipitation, sedimentation, and volatilization, can be involved. Investigating these processes is beneficial for the enhancement of the performance of NBSs. The present study provides a comprehensive review of factors that can influence nitrogen removal in different types of NBSs, and the possible strategies for nitrogen recovery that have been reported in the literature.