One of the possible ways to improve the operation efficiency of constructed wetlands and to prevent their clogging is the application of earthworms. They have already been successfully applied for vermicomposting and for sludge dewatering and treatment. A few studies have already examined the effect of earthworms on the treatment of wastewater by vertical flow constructed wetlands (VFCWs), but none of them have provided a yearlong research result from an open-air system or compared the effect that different seasons in a temperate climate area can have on these invertebrates. The goal of this research was to estimate the effect that earthworms and plants have on VFCW's operation. Four mesocosms (a filter, a filter with earthworms, a VFCW and a VFCW with earthworms) were built and their influent and effluent water quality was monitored for a period of 1 year. They were fed with wastewater coming from a building of the University of Bologna (Italy). The results have shown that the presence of earthworms in this specific system did not reduce the organic matter content of the substrate, but it has positively influenced plants' growth. However, since neither earthworms nor plants had a statistically significant effect on the effluent quality, it can be concluded that the integration of these invertebrates cannot improve wastewater treatment of vertical flow filters or constructed wetlands.

• Keywords
• Constructed wetlands, Earthworms, Filters, Plants, Seasonal effect, Wastewater treatment,
• MeSH
• Water Quality MeSH
• Wetlands MeSH
• Waste Disposal, Fluid methods   MeSH
• Wastewater chemistry   MeSH
• Sewage MeSH
• Oligochaeta physiology   MeSH
• Universities MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Italy MeSH
• Names of Substances
• Waste Water MeSH
• Sewage MeSH

Sludge treatment beds (STBs) have been used widely in many countries due to low energy consumption, low operating and maintenance costs, and better environmental compatibility. Penetration, evaporation, and transpiration are the main processes for sludge dewatering in STBs. However, the leachate quality from STBs usually cannot meet discharge limits. Moreover, such leachate has very low COD/N ratio, which makes it difficult to treat. In the present study, two subsurface flow (SSF) constructed wetlands (CWs) were investigated for the treatment of leachate from STBs under three different hydraulic retention time (HRT) (3 days, 4 days, 6 days), aiming for evaluating the effects of plants and HRT on treatment performance, as well as the potential of SSF CWs to treat sludge leachate with low COD/N ration. The results showed that plants play an important role in leachate treatment. The best treatment performance was achieved with HRT of 4 days. In this condition, the mean removal efficiencies of COD (chemical oxygen demand), NH4+-N, TN (total nitrogen), and TP (total phosphorus) in the planted and the unplanted CWs were 61.6% (unplanted - 3.7%), 76.6% (unplanted 43.5%), 70% (unplanted 41%), and 65.6% (unplanted 6%), respectively. Heavy metal concentrations were below the Chinese integrated wastewater discharge standard during the experimental period in the planted CW, and the removal efficiencies in the planted CW system were higher than in the unplanted CW system. In all, planted SSF CWs can be an effective approach in removing leachate from sludge treatment beds. Furthermore, considering to temperature and seasonal variation, the leachate from STBs needs to be further studied in pilot- and full-scale condition.

• Keywords
• Constructed wetland, Sludge leachate, Sludge treatment beds, Water purification,
• MeSH
• Water Purification MeSH
• Nitrogen analysis   MeSH
• Phosphorus analysis   MeSH
• Water Pollutants analysis   MeSH
• Biological Oxygen Demand Analysis MeSH
• Wetlands * MeSH
• Waste Disposal, Fluid methods   MeSH
• Wastewater MeSH
• Sewage MeSH
• Plants MeSH
• Metals, Heavy MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Nitrogen MeSH
• Phosphorus MeSH
• Water Pollutants MeSH
• Waste Water MeSH
• Sewage MeSH
• Metals, Heavy MeSH