Evaluation of the giant reed (Arundo donax) in horizontal subsurface flow wetlands for the treatment of dairy processing factory wastewater

Treatment of tequila vinasse mixed with domestic wastewater in two types of constructed wetlands

Tequila vinasse (TV) is a high-strength effluent generated during the production of tequila, with a chemical oxygen demand (COD) concentration of up to 74 g/L. In this study, the treatment of TV was evaluated in a 27-week study in two types of constructed wetlands (CWs), namely horizontal subsurface flow wetlands (HSSFWs) and vertical upflow wetlands (VUFWs). The pre-settled and neutralized TV was diluted at 10, 20, 30, and 40% with domestic wastewater (DWW). Volcanic rock (tezontle) was used as the substrate and Arundo donax and Iris sibirica as emergent vegetation. The two systems showed similar high removal efficiencies for COD, biochemical oxygen demand (BOD₅), turbidity, total suspended solids (TSS), true colour (TC), electrical conductivity (EC), and total nitrogen (TN). The highest average percentages of removal were obtained at 40% of dilution: 95.4 and 95.8% for COD, 98.1 and 98.2% for turbidity, 91.8 and 95.9% for TSS, and 86.5 and 86.4% for TC in the HSSFWs and the VUFWs, respectively. This study demonstrates the potential of CWs for TV treatment as a major step in a treatment system.

Biochar-amended constructed wetlands for eutrophication control and microcystin (MC-LR) removal

Microcystins (MCs) pollution caused by eutrophication and climate change has posed a serious threat to ecosystems and human health. Constructed wetlands (CWs) with biochar addition volume ratios of 0% (BC0-CWs), 10% (BC10-CWs), 20% (BC20-CWs) and 50% (BC50-CWs) were set up to evaluate the efficiency of biochar-amended CWs for eutrophication and MCs pollution control. The results illustrated that removal efficiencies of both NH₄⁺-N and NO₃^--N were enhanced by biochar addition to varying degrees. The average TP and MC-LR removal efficiencies increased with increasing biochar addition ratios, and the average TP and MC-LR removal efficiencies in biochar-amended CWs were significantly (p < 0.05) improved by 5.64-9.58% and 10.74-14.52%, respectively, compared to that of BC0-CWs. Biochar addition changed the microbial community diversity and structure of CWs. The relative abundance of functional microorganisms such as Burkholderiaceae, Nitrospiraceae, Micrococcaceae, Sphingomonadaceae and Xanthomonadaceae was promoted by biochar addition regardless of addition ratios. The higher relative abundance of the above microorganisms in BC20-CWs and BC50-CWs may contribute to their better removal performance compared to other CWs. The concentrations of extracellular polymeric substance (EPS) in biochar-amended CWs were significantly (p < 0.05) lower than that in BC0-CWs, which can reduce the risk of system clogging. This study demonstrated that biochar addition may be a potential intensification strategy for eutrophication and MCs pollution control by CWs. Considering both the removal performance and economic cost, a biochar addition ratio of 20% was recommended as an optimal addition ratio in practical application.

Comparison of heavy metal and nutrients removal in Canna indica and Oryza sativa L. based constructed wetlands for piggery effluent treatment in north-central Nigeria

Batch-fed horizontal sub-surface flow constructed wetlands (HssFCW) were developed to compare the potential of Canna indica and Oryza sativa L. in removing heavy metals and nutrients from piggery effluent. Piggery effluent samples were characterized for nutrients (N and P) and metals (Mg, Al, Ca and Fe) before and after introducing them to the HssFCW with hydraulic retention time (HRT) of 3 days and operational flowrate of 0.014 m³/day. Three sets of constructed wetlands (CWs) were monitored during the dry season for 3 months. The bioconcentration factor (BCF) and translocation factor (TF) for the plants were evaluated. The results were all significantly different at p ≤ 0.05. O. sativa L removes more nutrients and metals than C. indica. The BCF for O. sativa L. was higher than for C. indica, while the TF for C. indica was higher for O. sativa L., indicating a higher metal translocation potential. Use of C. indica, a non-food crop, poses no health risks in HssFCWs whereas the grains of O. sativa L. are consumed directly by humans, presenting potential risks when used in HssFCWs. Compared to an annual O. sativa L., the perennial C. indica can be grown continuously in CWs for the phytoremediation of piggery effluent. Novelty statementNo known work about the phytoremediation potential of the two studied macrophytes in the agro-ecological zone is known. The study also provides insight into the bioconcentration of metals in the edible part of Oryza sativa L. FARO 44 (SIPI 692033).The characterization of piggery effluent revealed that its compositions were above the allowable limit for reuse and recycling despite the adoption of low-water use intensive method.The study showed that Oryza sativa L accumulates more metals in the above-ground tissues than in its root and provide insight into its use as a phytoremediation plant in the study area.The footprint of pollutants and metals in Oryza sativa L makes a perennial C. indica more suitable than O. sativa L. in piggery effluent phytoremediation.

Treatment of microcystin (MC-LR) and nutrients in eutrophic water by constructed wetlands: Performance and microbial community

Cyanobacterial harmful algal blooms and microcystins (MCs) pollution pose serious threat to aquatic ecosystem and public health. Planted and unplanted constructed wetlands (CWs) filled with four substrates (i.e., gravel (G-CWs), ceramsite (C-CWs), iron-carbon (I-CWs) and slag (S-CWs)) were established to evaluate nutrients and a typical MCs variant (i.e., MC-LR) removal efficiency from eutrophic water affected by the presence of plant and different substrate. The response of the microbial community to the above factors was also analyzed in this study. The results indicate that the presence of plant can generally enhance nutrients and MC-LR removal efficiency in CWs, except for I-CWs. Throughout the experiment, all CWs exhibited good nitrogen removal efficiency with removal percentages exceeding 90%; TP and MC-LR average removal efficiency of C-CWs and I-CWs were greater than G-CWs and S-CWs irrespective of the presence of plant. The best MC-LR removal efficiency under different MC-LR loads was observed in planted C-CWs (ranged from 91.56% to 95.16%). Except for I-CWs, the presence of plant can enhance relative abundances of functional microorganisms involved in nutrients removal (e.g., Comamonadaceae and Planctomycetaceae) and MCs degradation (e.g., Burkholderiaceae). The microbial community diversity of I-CWs was simplified, while the relative abundance of Proteobacteria was highest in this study. The highest relative abundances of Comamonadaceae, Planctomycetaceae and Burkholderiaceae were observed in planted C-CWs. Overall, ceramisite and iron-carbon were more suitable to be applied in CWs for nutrients and MC-LR removal. This study provides a theoretical basis for practical application of CWs in eutrophication and MCs pollution control.

Selection of macrophytes and substrates to be used in horizontal subsurface flow wetlands for the treatment of a cheese factory wastewater

The aims of this study were to select the most suitable macrophyte species and substrate to be used in horizontal subsurface flow (HSSF) wetlands for the treatment of a local cheese factory wastewater, and to quantify the influence of plant species and substrates by applying of a simple first-order kinetic model. Microcosms-scale HSSF wetlands were planted with Canna glauca or Typha domingensis. LECA and river stones were used as substrates. Both studied macrophytes showed a high tolerance to the treated wastewater. HSSF wetlands were efficient for the treatment of diluted cheese production wastewater. COD, TP, NH₄⁺-N and TN showed high removal efficiencies in all the HSSF wetlands. HSSF wetlands planted with C. glauca showed the best performance for removal of NH₄⁺-N. The highest SRP removal was obtained in HSSF wetlands planted C. glauca with LECA as substrate. A simple first-order kinetics model was applied. The fitted parameters of the modified first-order model k-C* allowed to demonstrate the effect of the plants in the treatment of the effluent. HSSF wetlands planted with C. glauca using river stones were the systems that showed the fastest TIN removal. According to the obtained results, it is proposed to use C. glauca and river stones as substrate in a HSSF wetland for the treatment of this wastewater. The present study provides useful data to design a wetland at a larger scale.

Effect of plants in constructed wetlands for organic carbon and nutrient removal: a review of experimental factors contributing to higher impact and suggestions for future guidelines

Constructed wetland is a proven technology for water pollution removal, but process mechanisms and their respective contribution are not fully understood. The present review details the effect of plants on removal efficiency of constructed wetlands by focusing on literature that includes experiments with unplanted controls for organic carbon and nutrient (N and P) removal. The contribution of plant direct uptake is also assessed. Although it was found that several studies, mostly at laboratory or pilot scales, showed no statistical differences between planted and unplanted controls, some factors were found that help maximize the effect of plants. This study intends to contribute to a better understanding of the significance of the effect of plants in a constructed wetland, as well as to suggest a set of experimental guidelines in this field.

Effect of Increasing Salinity on Development of Giant Reed (Arundo donax) from Rhizome and Culms

Arundo donax (giant reed) has great potential for bioenergy biomass production in constructed wetlands. Large scale use of A. donax in constructed wetlands will require the use of either established plants sourced from nurseries, or the use of cuttings or rhizomes and stems from mother plants derived from nurseries or wild stands. The results of this study suggest that cuttings and rhizomes are not sensitive to salinity up to an EC ~ 4500 µS cm^- 1. Plants used to establish a constructed wetland should have stems of at least 300 mm length, with well established roots. Moreover, culms will emerge from small pieces of stems with viable nodes regardless of salinity, albeit the fresher the water the less likely salinity will subsequently affect the emerging shoot. From a practical perspective, this suggests that wetlands can be planted with giant reed using horizontally laid stems. Unless using plants pre-stressed to a salinity matching that of the wastewater to be treated, giant reed should be established using reasonable quality water (EC < 1000 µS cm^- 1) until the plants are of a reasonable size, e.g. > 500 mm in height, after which undiluted wastewater can be used.

A novel horizontal subsurface flow constructed wetland: Reducing area requirements and clogging risk

The use of Constructed Wetlands (CWs) has been nowadays expanded from municipal to industrial and agro-industrial wastewaters. The main limitations of CWs remain the relatively high area requirements compared to mechanical treatment technologies and the potential occurrence of the clogging phenomenon. This study presents the findings of an innovative CW design where novel materials were used. Four pilot-scale CW units were designed, built and operated for two years. Each unit consisted of two compartments, the first of which (two thirds of the total unit length) contained either fine gravel (in two units) or random type high density polyethylene (HDPE) (in the other two units). This plastic media type was tested in a CW system for the first time. The second compartment of all four units contained natural zeolite. Two units (one with fine gravel and one with HDPE) were planted with common reeds, while the other two were kept unplanted. Second cheese whey was introduced into the units, which were operated under hydraulic residence times (HRT) of 2 and 4 days. After a two-year operation and monitoring period, pollutant removal rates were approximately 80%, 75% and 90% for COD, ammonium and ortho-phosphate, respectively, while temperature and HRT had no significant effect on pollutant removal. CWs containing the plastic media achieved the same removal rates as those containing gravel, despite receiving three times higher hydraulic surface loads (0.08 m/d) and four times higher organic surface loads (620 g/m²/d). This reveals that the use of HDPE plastic media could reduce CW surface area requirements by 75%.

Sono assisted electrocoagulation process for the removal of pollutant from pulp and paper industry effluent

In the present work, the efficiency of the sonication, electrocoagulation, and sono-electrocoagulation process for removal of pollutants from the industrial effluent of the pulp and paper industry was compared. The experimental results showed that the sono-electrocoagulation process yielded higher pollutant removal percentage compared to the sonication and electrocoagulation process alone. The effect of the operating parameters in the sono-electrocoagulation process such as electrolyte concentration (1-5 g/L), current density (1-5 A/dm²), effluent pH (3-11), COD concentration (1500-6000 mg/L), inter-electrode distance (1-3 cm), and electrode combination (Fe and Al) on the color removal, COD removal, and power consumption were studied. The maximum color and COD removal percentages of 100 and 95 %, respectively, were obtained at the current density of 4 A/dm², electrolyte concentration of 4 g/L, effluent pH of 7, COD concentration of 3000 mg/L, electrode combination of Fe/Fe, inter-electrode distance of 1 cm, and reaction time of 4 h, respectively. The color and COD removal percentages were analyzed by using an UV/Vis spectrophotometer and closed reflux method. The results showed that the sono-electrocoagulation process could be used as an efficient and environmental friendly technique for complete pollutant removal.

Role of three different plants on simultaneous salt and nutrient reduction from saline synthetic wastewater in lab-scale constructed wetlands

Constructed Wetlands (CWs) can be a valuable technology to treat high salinity wastewaters but it is not known their potential for removal of both nutrients and salt, and the type of plants to use. This study evaluated the effect of three plants on salt reduction and simultaneous nutrient removal in CWs microcosms with expanded clay and in hydroponic conditions. Initial values of the synthetic wastewater tested were EC=15dSm^-1, SAR=151; NH₄⁺-N=24mgL^-1; PO₄^3--P=30mgL^-1 and NO₃^--N=34mgL^-1. With expanded clay CW removal efficiency for NH₄⁺-N was 21, 88 and 85%, while for NO₃^--N, it was 4, 56 and 68% for Spartina maritima, Juncus maritimus and Arundo donax, respectively. PO₄^3--P was adsorbed completely in the expanded clay. However, in hydroponic system, removal efficiencies for NH₄⁺-N were 53 and 50%, while PO₄^3--P removal was 89 and -14% for Spartina maritima and Juncus maritimus, respectively. Nutrient removal in planted microcosms was statistically higher than unplanted controls for NH₄⁺-N and PO₄^3--P. However, salt removal was apparent in the hydroponic system only after 23days of HRT, despite clear salt excretion visible in both Spartina maritima and Juncus maritimus. This study demonstrates the potential of two halophytic plants for saline wastewater treatment. However, salt removal in such a scenario could not be well documented and might prove to be impractical in future work.

Sodium uptake of Iris wilsonii and its photosynthetic responses to high-salinity stress in microcosm submerged beds

In order to investigate the performance of Iris wilsonii in high-salinity wastewater, seven microcosm submerged beds were built with rectangular plastic tanks and packed with marble chips and sand. Each submerged bed was transplanted with six stems of I. wilsonii. The submerged beds were operated in a 7-d batch mode in a greenhouse with artificial wastewater for three 42-d periods. Influent to the seven submerged beds had different contents of NaCl, 0, 1, 2, 4, 6, 8, and 10% (by weight). The results suggested that lower salinity contents (1-2%) in influent or during short stress time (0-14d) did not inhibit net photosynthetic rate, stomatal conductance, and transpiration rate of I. wilsonii, and the chlorophyll of I. wilsonii was not damaged. When initial NaCl contents were at 4% and above, however, all photosynthetic parameters were significantly decreased. It was concluded that I. wilsonii could take up Na⁺ in wastewater, but higher salinity (4-10%) in wastewater would inhibit the growth of I. wilsonii.