The main operational problem of subsurface flow constructed wetlands (CWs) is clogging of granular medium, a phenomenon related to the accumulation of different types of solids that lead to a reduction of the infiltration capacity of the gravel bed. It is generally accepted that the application of a good wastewater pretreatment is essential for the long‐term operation of subsurface flow CW. Anaerobic digesters (ADs) could help to the aim of clogging prevention. Two combined AD‐CW treating either municipal or winery wastewater were designed and monitored for trough performance and efficiency parameters, solids accumulation and hydraulic conductivity, over a long term period. CW operated at high organic loading rates in terms of TCOD and BOD5 while suspended solids loading rates and solids accumulation in CW were lower. In turn, CW maintained an adequate hydraulic conductivity and low rates of solids accumulation.
The objective of the present study was to investigate for the first time the long‐term removal of heavy metals (HMs) in a combined UASB‐CW system treating municipal wastewater. The research was carried out in a field pilot plant constituted for an upflow anaerobic sludge bed (UASB) digester as a pretreatment, followed by a surface flow constructed wetland (CW) and finally by a subsurface flow CW. While the UASB showed (pseudo) steady state operational conditions and generated a periodical purge of sludge, CWs were characterised by the progressive accumulation and mineralisation of retained solids. This paper analyses the evolution of HM removal from the water stream over time (over a period of 4.7 year of operation) and the accumulation of HMs in UASB sludge and CW sediments at two horizons of 2.7 and 4.0 year of operation. High removal efficiencies were found for some metals in the following order: Sn > Cr > Cu > Pb > Zn > Fe (63–94%). Medium removal efficiencies were registered for Ni (49%), Hg (42%), and Ag (40%), and finally Mn and As showed negative percentage removals. Removal efficiencies of total HMs were higher in UASB and SF units and lower in the last SSF unit.
Composting of solid fraction of swine manure is a usual practice in most farms in order to obtain a fertilizer of better quality. Due to the negative hydric balance of the composting process, watering the composting material is necessary, what may be carried out with liquid fraction of pig manure. In this way, substantial amounts of liquid fraction can be treated by composting, allowing the recovering the nutrients and reducing the volumes to be transported to the more distant crop fields or subjected to further treatment. Thus, the main objective of this research was to study the treatment of liquid fraction of pig manure by co‐composting with solid fraction of pig manure and other solid biowaste generated in rural areas. The present research is part of a project to find an integral solution for pig manure consisting of nutrient recovery through compost production and water re‐use after biological purification in constructed wetlands. In accordance with the European waste management hierarchy, sustainable and low cost cleaner technologies aiming at resource recovery must be developed as an alternative to conventional technologies applied to the treatment of pig manure. This paper presents the results of composting of liquid fraction of fresh manure, which is conceived at the same time as a pig wastewater pre‐treatment, wastewater volume reduction and a nutrient recovery system. Two 30 m3 turned windrows were constituted with solid fraction of pig manure and Populus sp. wood chips as bulking material at volume ratios of 1:1 and 1:2 and watered intensely with liquid fraction whilst thermophilic temperatures were maintained. Subsequently, both windrows were divided and the new windrows each received the same quantity of a different organic waste (solid fraction of pig manure, sawdust and grape bagasse), being watered with liquid fraction for a further 30 days. Stabilised composts with a nitrogen content ranging from 1.8 to 2.0% and a carbon to nitrogen ratio from 14.0 to 18.8 were obtained. Water balances showed evaporation rates ranging from 14 to 76 L/t total solids∙d and overall evaporation ratios from 1‐2.7 m3/t total solids, referred to dry matter of solid waste. While the reduction of liquid fraction volume ranged from 58 to 88% (depending on the watering rate), mass reduction of pollutants reached approximately 90% of total Kjeldahl nitrogen, ammonium and suspended solids. In comparison with traditional composting processes of solid fraction, our results show that huge amounts of liquid fraction can be treated by co‐composting with solid fraction and other solid wastes. Integrating the liquid fraction of pig manure in the composting process has improved the compost quality and has reduced the pollutant load in the remaining liquid fraction, which makes possible an advanced treatment in constructed wetlands in order to reach the necessary water quality to be recycled or even to discharge in natural water bodies. In this way, both composting and constructed wetland systems can offer an integral solution for the recovery of water and fertilizer elements contained in pig manure and diverse locally generated solid wastes. However, in spite of these benefits, more research focusing on nitrogen balances, ammonia volatilisation and greenhouse emissions will be of great interest.
An integral solution for the recovery of fertilizer elements contained in swine farm slurry is the joint com‐posting of diverse solid wastes generated in the installation and surroundings, in which the composting material was watered with swine slurry. In such a system, a high percentage of the water contained in the slurry is evaporated while nutrients are, in part, retained in the compost produced. This paper presents the results of a pilot vertical flow constructed wetland (VFCW) treating the high strength leachate generated from the compost piles. The VFCW was provided with effluent recycling in order to deal with high influent concentrations of nitrogen compounds, which reached up to 459 mg NH3‐N/L and 904 mg TKN/L without the need for dilution with clean water. After start‐up, and operating at 10 C with surface loading rates (SLRs) of 9.2, 17.9, 4.8 and 1.9 g/m2 d of TSS, TCOD, BOD5 and TN, respectively, the VFCW reduced the concentration of all these parameters by more than 93%. Effluent concentration of nitrate was high during the two first months of operation (178 mg NO3‐N/L), but afterwards simultaneous nitrification and denitrification developed, reaching total nitrogen removal of 93% and low effluent nitrogen concentration (16 mg NH3‐N/L and 10 mg NO3‐N/L). Furthermore, options to avoid clogging or to facilitate the application of higher SLR are discussed.
A full‐scale hybrid constructed wetland (CW) was built to treat mixed effluent derived from a winery and tourist establishment. The treatment system consisted of a hydrolytic upflow sludge bed (HUSB) digester for suspended‐solids removal, a vertical‐flow constructed wetland (VF) and three parallel subsurface horizontal‐flow constructed wetlands (HF). The HUSB reduced TSS loads to 72‐172 mg L‐1, helping to prevent clogging, while organic loads for the wastewater entering the VF ranged from 422 to 2178 mg COD L‐1 and from 216 to 1379 mg BOD5 L‐1. At an average hydraulic loading rate (HLR) of 19.5 mm d‐1 and average surface loading rates (SLR)
of 30.4 g COD m‐2 d‐1 and 18.4 g BOD5 m‐2 d‐1, the overall VF+HF CW system reached average removal efficiencies of 86.8% of TSS, 73.3% of COD, and 74.2% of BOD5. The system also removed 52.4% of total Kjeldhal nitrogen (TKN), 55.4% of NH3‐N and 17.4% of phosphates. While the VF unit showed high removal rates, the HF unit operated at lower removal rates than those previously reported. The CW units showed rapid adaptation to low pH values. A linear‐regression analysis indicated that the independent variables SLR and temperature determined more than 95% of the variation in performance and efficiency of the CW system and offered simple mathematical models for design and system‐description purposes.
A comparative long‐term study of three subsurface horizontal‐flow (HF) constructed wetlands (CW) treating winery wastewater was carried out. The water depth for HF1 was 0.3 m, while the depth for HF2 and HF3 was 0.6 m, respectively. Hydraulic loading rate ranged from 7 to 93 mm/d, while surface loading rates fell into the following ranges: 4–85 g COD/m2∙d, 2–49 g BOD5/m2∙d and 0.5–6 g TSS/m2∙d. The percentage of biological oxygen demand (BOD5) removal clearly decreased when influent concentration increased, while surface removal rate increased and reached a maximum of approximately 8 g BOD5/m2∙d removed in the range of 10–20 g
BOD5/m2∙d fed, depending on the CW depth. HF1 showed a worse performance than the other units, appearing to be more affected by high influent concentrations. Solids accumulation on gravel media, hydraulic conductivity and gas emissions were monitored over the 2.8 years of operation.