Use of ornamental plants in floating treatment wetlands for greywater treatment in urban areas.

Floating treatment wetlands are considered a promising and low-cost technology for the treatment of polluted water and wastewater. However, their functionality and efficiency in different types of wastewater are not fully understood. In this study, several ornamental plant species (monocultures: Canna sp., Iris sp., polyculture: Iris orientalis, Cyperus sp., Acorus gramineus) were tested in two different types of floating mats, including a media supported floating mat (MSFM) or a simple plastic grid, and evaluated for optimal removal of the studied pollutants. The results regarding pollutant removal revealed that planted systems grown in MSFM achieved significantly higher removal rates (up to 90 %) compared to the plastic grid (up to 80 %). Statistically significant higher removal rates were obtained for the planted systems compared to the unplanted systems either grown in MSFM (for turbidity (planted: 82-90 %; unplanted: 44 %), COD (planted: 74-84 %; unplanted: 32 %) and BOD5 (planted: 76-85 %; unplanted: 51 %), respectively) or grown in the plastic grid (for turbidity (planted: 64-78 %; unplanted: 44 %) and COD (planted: 43-75 %; unplanted: 32 %), respectively). During the experimental period (7 months), all plants managed to survive and withstand the weather variations. The plants in polyculture followed by Iris sp. plants in plastic grid floating mats were better adapted, as indicated by maximum quantum efficiency of PSII values and chlorophyll content index, while all the plants were considered well adapted in the MSFM. Overall, the implementation of floating treatment wetlands with ornamental vegetation for greywater treatment in urban areas seems to be a sustainable and efficient approach.

Leachate management in medium- and small-sized sanitary landfills: a Greek case study.

The sustainable management of landfill leachates remains a matter of important concern in many countries. We used as case study a medium-sized Greek landfill, and we initially investigated the performance of the existing secondary leachate treatment system. The activated sludge process removed chemical oxygen demand (COD), biochemical oxygen demand (BOD), NH4-N, and PO4-P by 55%, 84%, 94%, and 14%, respectively, but the effluents did not meet the legislation requirements for discharge or reuse. Afterwards, different management options of these effluents (co-treatment with sewage in the centralized treatment plant, onsite tertiary treatment with reverse osmosis, granular activated carbon (GAC), ozonation, photo-Fenton, or constructed wetlands) were evaluated regarding their operational costs and environmental footprint. The use of constructed wetlands presented the lower operational cost, energy requirements, and greenhouse gas (GHG) emissions, not exceeding 21.5 kg CO2eq/day. On the other hand, the power consumption and the GHG emissions of the other on-site technologies ranged from 0.37 kWh/m3 and 5.56 kg CO2eq/day (use of GAC) to 39.19 kWh/m3 and 588.6 kg CO2eq/day (use of ozonation), respectively. The co-treatment of the leachates with municipal wastewater required 0.6 kWh/m3 and emitted 30.18 kg CO2eq/day. For achieving zero-discharge of the treated leachates, a system consisting of constructed wetlands and evaporation ponds in series was designed.

Granular activated carbon stimulates biogas production in pilot-scale anaerobic digester treating agro-industrial wastewater.

This work examines the continuous addition (5 g/L) of conductive granular activated carbon (GAC) in an integrated pilot-scale unit containing an anaerobic digester (180 L) and an aerobic submerged membrane bioreactor (1600 L) connected in series for the treatment of agro-industrial wastewater. Biogas production increased by 32 % after the addition of GAC. Methanosaeta was the dominant methanogen in the digester, and its relative abundance increased after the addition of GAC. The final effluent after post-treatment with the aerobic membrane bioreactor had a total solids content <0.01 g/L and a chemical oxygen demand between 120 and 150 mg/L. A simple cost analysis showed that GAC addition is potentially profitable, but alternatives ways of retaining the GAC in the system need to be found. Overall, this study provides useful scientific data for the possible application of GAC in full-scale biogas projects.

Removal of pathogens from greywater using green roofs combined with chlorination.

Greywater is an important alternative water resource which could be treated and reused in buildings, reducing the freshwater demand in drought affected areas. For the successful implementation of this solution, it is important to ensure the microbial safety of treated greywater. This study examined the microbiological quality of treated greywater produced by an emergent nature-based technology (green roofs) and a chlorination process. Specifically, the effect of substrate, substrate depth, and vegetation on the removal of total coliforms, Escherichia coli, and enterococci in experimental green roofs treating greywater was examined for a period of about 12 months. In addition, the ability of chlorination to inactivate the abovementioned pathogen indicators was evaluated and their potential regrowth was examined. Results shown that green roofs filled with 10 cm of perlite reduce total coliform concentration by about 0.4 log units while green roofs filled with 20 cm of vermiculite reduce total coliform concentration by about 1.2 log units. In addition, the use of vegetation in green roofs improves the removal of pathogenic bacteria by about 0.5 log units in comparison with unvegetated systems. In all cases, the effluents of green roofs failed to satisfy the criteria for indoor reuse of treated greywater for non-potable uses such as toilet flushing without a disinfection process. The addition of 3 mg/L of chlorine in the effluent provided safe greywater microbiological quality for storage periods of less than 24 h, while longer periods resulted in the significant regrowth of pathogens. In contrast, a chlorination dose of 7 mg/L completely secured inactivation of pathogen indicators for periods of up to 3 days.

Comparing the use of a two-stage MBBR system with a methanogenic MBBR coupled with a microalgae reactor for medium-strength dairy wastewater treatment.

Two systems were compared for medium-strength dairy wastewater treatment. The first comprised a methanogenic Moving Bed Biofilm Reactor (AnMBBR) and an aerobic MBBR (AeMBBR), while the second an AnMBBR and a sequencing batch reactor (SBR) with Chlorella sorokiniana. The AnMBBR, under ambient conditions, achieves biogas production sufficient enough to attain energy autonomy. The produced energy was 0.538 kWh m-3, whereas the energy consumption 0.025 kWh m-3. Its coupling with the AeMBBR removed COD, NH4-N TKN, and PO4-P by 93 ± 4%, 97 ± 3%, 99 ± 1% and 49 ± 15%, respectively, while the use of the SBR as a second step eliminated totally COD but partially the other pollutants. The higher nitrogen removal in the first system was due to nitrification occurring in the AeMBBR. The acclimatization of microalgae to dairy wastewater enhanced their growth. Their protein content was 54.56%, while starch and lipids were 3.39% and 23.1%, respectively.