Treatment of swine wastewater with subsurface-flow constructed wetlands in Yucatán, Mexico: Influence of plant species and contact time

This study evaluates the capability of horizontal subsurface-flow constructed wetlands (SSF CWs) for treating pretreated swine wastewater as a function of contact time (CT) and type of macrophyte under the local conditions of Yucatán, Mexico. Experiments were conducted from July 2004 to November 2005 on a swine-fattening farm. The study had three stages: first, macrophytes were located and collected; second, plants were acclimatised; and third, a pilot plant with 6 wetlands was set up, operated and evaluated. The effectiveness of the wetlands was intensively tested over 2 periods (April and November 2005). The results indicate that treatment efficiency significantly improved with increased CT for most of the analysed contaminants. The highest removal rates were recorded at a CT of 3 d and ranged between 64 and 78% for total suspended solids, 52 and 78% for COD, 57 and 74% for BOD5, 57 and 79% for total nitrogen, 63 and 75% for ammonium nitrogen, 70 and 81% for nitrate, 0 and 28% for total phosphorus and 3.3 and 4.2 log-units for total coliforms. Results also suggest that the macrophyte species used did not significantly differ on their contribution to overall treatment efficiency. However, vegetated beds slightly improved water quality when compared to unplanted systems. Horizontal SSF CWs are a suitable technology for treating swine wastewater under the local conditions of Yucatán. Contact time should be given special attention in the design of future full-scale facilities

Advances in automated reed bed installations

Constructed wetlands are a popular form of waste-water treatment that have proliferated across Europe and the rest of the world in recent years as an environmentally conscious alternative to chemical treatments. The ability to monitor the conditions in the bed and control input factors such as heating and aeration may extend the lifetime of the reed bed substantially beyond the ten year lifetime normally reached. The Autonomous Reed Bed Installation (ARBI) project is an EU FP7 initiative to develop such a bed. One critical parameter to observe is the clog state of the reed bed, as this can severely impact on the efficiency of water treatment. Magnetic resonance (MR) sensors can be a powerful tool in determining clogging levels (Analyst 2011, 136, 2283-2286) and allow automated remedial action to be taken against the bed improving treatment efficiency, prolonging the life of the bed and avoiding the need to refurbish the bed, which is both time consuming and costly. This work details magnetic sensors suitable for long-term embedding into a constructed wetland

Advances in clog state monitoring for use in automated reed bed installations

Constructed wetlands are a popular form of waste-water treatment that have proliferated across Europe and the rest of the world in recent years as an environmentally conscious form of waste water treatment. The ability to monitor the conditions in the bed and control input factors such as heating and aeration may extend the lifetime of the reed bed substantially beyond the ten year lifetime normally reached. The Autonomous Reed Bed Installation (ARBI) project is an EU FP7 initiative to develop a reed bed with automated control over input parameters based on readings taken from embedded sensors. Automated remedial action may improve bed treatment efficiency, and prolong the life of the bed and avoiding the need to refurbish the bed, which is both time consuming and costly. One critical parameter to observe is the clog state of the reed bed, as this can severely impact on the efficiency of water treatment to the point of the bed becoming non-operable. Magnetic resonance (MR) sensors can be a powerful tool in determining clogging levels, and has previously been explored in the literature. This work is based on a conference paper (2nd International Conference "Water resources and wetlands", 2014) and details magnetic sensors suitable for long-term embedding into a constructed wetland. Unlike previous studies this work examines a probe embedded into a wetland

Intermittent aeration to improve wastewater treatment efficiency in pilot-scale constructed wetland

Forced aeration of horizontal subsurface flow constructed wetlands (HSSF CWs) is nowadays a recognized method to improve treatment efficiency, mainly in terms of ammonium removal. While numerous investigations have been reported testing constant aeration, scarce information can be found about the efficiency of intermittent aeration. This study aims at comparing continuous and intermittent aeration, establishing if there is an optimal regime that will increase treatment efficiency of HSSF CWs whilst minimizing the energy requirement. Full and intermittent aeration were tested in a pilot plant of three HSSF CWs (2.64 m2 each) fed with primary treated wastewater. One unit was fully aerated; one intermittently aerated (i.e. by setting a limit of 0.5 mg/L dissolved oxygen within the bed) with the remaining unit not aerated as a control. Results indicated that intermittent aeration was the most successful operating method. Indeed, the coexistence of aerobic and anoxic conditions promoted by the intermittent aeration resulted in the highest COD (66%), ammonium (99%) and total nitrogen (79%) removals. On the other hand, continuous aeration promotes ammonium removal (99%), but resulted in nitrate concentrations in the effluent of up to 27 mg/L. This study demonstrates the high potential of the intermittent aeration to increase wastewater treatment efficiency of CWs providing an extreme benefit in terms of the energy consumption

Assessing the economic suitability of aeration and the influence of bed heating on constructed wetlands treatment efficiency and life-span

Intensive constructed wetlands including forced aeration and heating were studied to improve treatment efficiency and prevent clogging. The experiments were carried out in a pilot plant (0.4 m2) treating urban wastewater with an organic loading rate of 40-60 gCOD/m2∙d. Continuous and intermittent aeration was performed on 8% of the wetland surface, leading to different dissolved oxygen concentrations within the wetlands (from 0.2 to 5 mgO2/L). Continuous forced aeration increased organic matter (COD) and ammonium nitrogen removal by 56% and 69%, respectively. Improvements in 33 wastewater treatment caused by forced aeration can result into reduction of the surface area. This work demonstrated that for the studied configuration the cost of the power consumption of the continuous aeration was largely covered by the reduction of the wetlands surface. Even if the heating of 8% of the wetland surface at 21°C had no effects on treatment performances, positive results showed that solids accumulation rate within the granular medium, which is closely related to the development of clogging. It has been demonstrated that heating for 10 days per year during 20 year period would delay the equivalent of 1 year of solids accumulation

A review of technologies for closing the P loop in agriculture runoff: contributing to the transition towards a circular economy

Phosphorus (P) scarcity and the environmental hazards posed by P discharges have triggered the development of technologies for P sequestration and removal from waste streams. Agriculture runoff usually has P concentrations high enough to contribute to eutrophication and harmful algal blooms, but they are still too low for successful P removal with conventional technologies commonly applied in wastewater treatment. For this reason, realistic approaches to remove P from agricultural waste streams mainly include natural assimilation and constructed wetlands. Although these technologies have been implemented for some time, P removal is not always achieved to the needed extent and sometimes sufficient surface areas required are unattainable. Phosphorus sorbing materials, especially materials rich in calcium, have emerged to increase the removal potential of runoff treatment wetlands and at the same time sequester P for potential subsequent reuse. This paper analyses the current strategies and technologies for P removal and reuse from agriculture surface runoff streams taking a circular economy approach. It particularly addresses the current state of calcium rich materials commonly used for P removal that have also shown positive results as fertilizers or soil.This work has been possible thanks to the European funding programme “Iniciativa de Empleo Juvenil” and the Spanish Ministry of Science and Innovation (project reference: PEJ2018-005586-A).Peer ReviewedPostprint (published version

Influence of tubificid worms on nutrient fluxes across water-sediment interface in fish farm settling ponds

The influence of tubificid worms on nutrient translocation from water to fish farm sediments accumulating in settling ponds was addressed under laboratory conditions. Small microcosms of 0.5 L were filled up with 35 g of sludge from a fish farm settling pond and 0.15 L of filtered settling pond water. The experimental set up consisted of one control line (no worms added), a second experimental line with 1 mg of tubificid worms·g-1 fresh sediment (550 individuals·m-2) and a third experimental line with 40 mg of tubificid worms·g-1 fresh sediment (22 000 individuals·m-2). Nutrients translocation was determined by monitoring overlaying water concentration of ammonia, nitrate and phosphate for ten days. Results showed that abundances of 550 individuals·m-2 had no significant influence on the fluxes of nutrients here considered. However, the influence of higher abundances of tubificids (22 000 individuals·m-2) was of significant extent on the translocation of nitrate and phosphate. Accordingly, bioturbation of tubificids caused 55% lower nitrate uptake by the sediment when compared to control conditions. Phosphorus released by the sediments of the control condition was ca. 90% higher than that recorded under abundances of tubificids (22 000 individuals·m-2). Results obtained allowed us to estimate that fish farm settling ponds highly colonized by tubificid worms (22 000 individuals·m-2) may contribute to decrease phosphorus discharge (in terms of soluble phosphorus) in ca. 5 g of P·ton-1 of fish produced