Substrate In Constructed Wetlands Research Articles

Evaluation of thermally-modified calcium-rich attapulgite as a low-cost substrate for rapid phosphorus removal in constructed wetlands

The cost-effective and geographically available substrates are vital for the design of constructed wetlands (CWs), especially the saturated subsurface flow CWs, which are deemed as an efficient way to remove the inlet-lake phosphorus concentrations. In this study, phosphorus removal of thermally-treated calcium-rich attapulgite (TCAP) with varied particle sizes (0.2–0.5 mm, 0.5–1 mm and 1–2 mm) was assessed using batch and long-term column experiments to evaluate its feasibility as a CWs substrate. The phosphorus-bound mechanism in TCAP was identified in various initial phosphorus concentrations. Batch studies indicated that more than 95% of P can be rapidly (<1 h) removed by TCAP from solution with a concentration of 20 mg P/L, and P sorption can be well fitted by a pseudo-second-order equation. The maximum P sorption capacity of TCAP was in the range of 4.46–5.99 mg P/g, and the availability of Ca2+ concentration might limit the P removal capacity of TCAP at high phosphorus concentrations. Both the P removal rate and capacities decreased with the increase of TCAP particle sizes. Column P removal experiments indicated that hydraulic retention time (HRT) exerts great influence on P removal performance and longer HRTs favor the dissolution of CaO in TCAP, consequently increasing the P removal rate. In a 150-day P removal experiment, TCAP removed an average of 93.1%–95.4% of the influent P with a HRT of eight hours. Both the batch and chemical extraction of the P fraction of TCAP showed that the P removed by TCAP was mainly through formation of Ca phosphate precipitation. However, the species of Ca-P precipitation formed might be varied in different phosphorus concentrations. All results indicated that TCAP can be a suitable substrate when used in CWs, and field experiments should be carried out to test its real P removal performance in the future.

Iron [Fe(0)]-rich substrate based on iron–carbon micro–electrolysis for phosphorus adsorption in aqueous solutions

The phosphorus (P) adsorption properties of an iron [Fe(0)]-rich substrate (IRS) composed of iron scraps and activated carbon were investigated based on iron–carbon micro-electrolysis (IC–ME) and compared to the substrates commonly used in constructed wetlands (CWs) to provide an initial characterization of the [Fe(0)]-rich substrate. The results showed that P was precipitated by Fe(III) dissolved from the galvanic cell reactions in the IRS and the reaction was suppressed by the pH and stopped when the pH exceeded 8.90 ± 0.09. The adsorption capacity of the IRS decreased by only 4.6% in the second round of adsorption due to Fe(0) consumption in the first round. Substrates with high Ca– and Mg–oxide contents and high Fe– and Al–oxide contents had higher P adsorption capacities at high and low pH values, respectively. Substrates containing high Fe and Al concentrations and low Ca concentrations were more resistant to decreases in the P adsorption capacity resulting from organic matter (OM) accumulation. The IRS with an iron scrap to activated carbon volume ratio of 3:2 resulted in the highest P adsorption capacity (9.34 ± 0.14 g P kg−1), with minimal pH change and strong adaptability to OM accumulation. The Fe(0)–rich substrate has the considerable potential for being used as a CW substrate.

Microbial density and diversity in constructed wetland systems and the relation to pollutant removal efficiency.

Microbes are believed to be at the core of the wastewater treatment processes in constructed wetlands (CWs). The aim of this study was to assess the microbial biomass carbon (MBC) and Shannon's diversity index (SDI) in the substrate of CWs planted with Phragmites australis, Hymenocallis littoralis, Canna indica and Cyperus flabelliformis, and to relate MBC and SDI to the pollutant removal in the systems. Significant higher MBC was observed in CWs with H. littoralis and C. indica than in CWs with P. australis, and the MBC differed with season and substrate depth. The microbial community in the wetlands included four phyla: Cyanobacteria, Proteobacteria, Chloroflexi, and Acidobacteria, with a more diverse community structure in wetlands with C. flabelliformis. The MBC in the substrate and the SDI of the 15-20 cm depth correlated with the removal of biochemical oxygen demand, NH4-N and NO3-N. Our results indicate that substrate SDI and MBC can both be regarded as bioindicators of the pollutant removal ability in CWs.

Comprehensive evaluation of substrates in vertical-flow constructed wetlands for domestic wastewater treatment

Substrates are the important component of constructed wetlands (CWs), which have an effect on construction cost, purification capability and stable operation, so that substrate optimization is the key part of CWs design. The comprehensive evaluation system, including four layers, eleven indicators and nine schemes, for substrates in vertical-flow CWs treating domestic wastewater was established based on analytic hierarchy process. Then combined with Delphi method and fuzzy synthetic evaluation approach, zeolite, anthracite, shale, vermiculite, ceramic filter material, gravel, steel slag, bio-ceramic and combination substrate (isopyknic layered anthracite, bio-ceramic and zeolite) were evaluated from the viewpoints of purification effect, practical performance and economic analysis. The results showed that phosphorus removal, nitrogen removal, chemical stability were the main factors of substrate selection. Combination substrate was the best scheme among nine substrates. Zeolite was ideal substrate for nitrogen removal and biocompatibility, while anthracite and steel slag were ideal substrates for phosphorus removal. The comprehensive evaluation system of substrates was beneficial to comprehensive compare all aspects of performance for different substrates, and could be improved according to the actual situation of engineering applications, so as to provide guidance of substrate selection for CWs design.

Potential of constructed wetlands microcosms for the removal of veterinary pharmaceuticals from livestock wastewater

The aim of the present work was to evaluate, at microcosm level, the capacity of constructed wetlands (CWs) to remove veterinary pharmaceutical compounds, from wastewater. Results indicated that CWs have potential to mitigate the release of veterinary drugs, namely enrofloxacin (ENR, a fluoroquinolone) and tetracycline (TET, tetracyclines family). Removal efficiencies of 94% and 98% where achieved for TET and ENR, respectively, when treating pigfarm wastewater effluent doped at 100μgL−1 drug level, along twelve weeks. Occurrence of adsorption of the drugs to CWs substrate may be the predominant mechanism for ENR, although for TET there are signs that degradation is also occurring.

Phosphorus recovery as AlPO 4 from beneficially reused aluminium sludge arising from water treatment

The purpose of this study was to develop an efficient and, possibly, a practically operated methodology to recover phosphorus (P) from P-saturated dewatered aluminium sludge cakes (DASC) after the DASC have been beneficially reused as constructed wetlands substrate for P-rich wastewater treatment. A three-step procedure of 1) P extraction by H 2SO 4, 2) decolorization of extraction leachate via H 2O 2 oxidation, and 3) AlPO 4 precipitation by pH adjustment, has been explored. The optimal conditions to form the precipitates of AlPO 4 were determined, with 97% of P and 99% of Al being recovered. The obtained compounds were identified by XRD, FTIR and SEM analyses. Although the purity, structure, characteristics and production control of the compounds are worthy of further investigation, this study provides a showcase of a ‘closed loop’ regarding the beneficial reuse of a ‘waste’ and the recovery of useful elements after the reuse.

INFLUENCING FACTORS OF LIMESTONE SORPTION AND ITS USAGE IN ADVANCED WASTEWATER TREATMENT FOR PHOSPHORUS REMOVAL

Phosphorus (P) is one of the main triggering nutrients responsible for eutrophication which troubles many waters in China. This study was to investigate the influencing factors of limestone (LS) adsorption and establish the parameter of constructed wetland (CW) using LS as the main substrate when treating effluent from a municipal wastewater treatment plant (MWTP) for P removal. First, a series of batch experiments were conducted to study the influencing factors of LS adsorption. Consequently, the P removal efficiency increased with the temperature and was high during the initial 3 h; the efficiency was over 75% even at initial P content 50 mg/L; under 2 mm small LS particle size enhanced the adsorption but the difference was not significant; the efficiency was over 90% when initial pH was below 6.37 and decreased sharply at pH above 8.15; sodium chloride as background electrolyte decreased the adsorption; organic acids including tartaric acid, oxalic acid and citric acid all suppressed the adsorption, and citric acid demonstrated the strongest effect. Then column experiment was conducted to evaluate the effect of the continuous vertical-flow LS bed treating effluent from a MWTP with varying hydraulic retention time (HRT). Over 80 days, the effluent pH was between 7 and 9, and effective running time increased with HRT during which the effluent total P content was below 0.5 mg/L. Short HRT such as 1 h or 1.5 h was recommended for dynamic LS adsorption. It showed that LS was suitable for the substrate in CW for P removal in wastewater advanced treatment.

Fragmented limestone wastes as a constructed wetland substrate for phosphorus removal

This study investigated the potential of fragmented Moleanos limestone (FML) as substrate in constructed wetlands for phosphorus removal. Being a waste material which results from industries of extraction and production of decorative stones for construction activities, FML is quite inexpensive. Laboratory experiments were performed in a packed bed column with recycle to test the FML's capacity to sorb phosphorus from a phosphate solution. The experimental data were found to follow the Langmuir model better than the Freundlich model. From the isotherm parameters obtained it can be concluded that the sorption capacity of FML is similar to those quoted in the literature for mineral materials. A subsurface flow constructed wetland filled with FML and planted with Phragmites australis was monitored during 20 months, at a mean hydraulic load of 40±4L/(m2day). Results demonstrated that average phosphorus removal efficiencies of 61%±7 can be achieved during the trial period, and a global first order kinetic constant of 0.062±0.001m/day was fitted to experimental data using the well mixed serial tanks model. Morphological aspects of reed growth were also studied and indicated high plant yield. The use of FML as a substrate media in constructed wetlands can be a promising solution in developing a cost effective, environmental friendly and sustainable technology for phosphorus removal, particularly where this material is readily available.

Different Constructed Wetland Substrates and their Applications

In recent years, constructed wetland technology as an alternative to conventional sewage treatment technology process has been widely used, industrial waste, agricultural waste, non-point source pollution control and reconstruction wetlands. Because the technology can remove organic pollutants and nitrogen and phosphorus and to beautify the environment has become widely accepted, the goal of this work was to provide different constructed wetland substrates and their applications. This study was designed to determine differences in the ability of different types of constructed wetland substrates.

Removal of Nutrients from Saline Waste Sewage with Different Vertical-Flow Constructed Wetland Substrates

In order to find the best substrates of constructed wetlands for saline waste sewage treatment, Bio-ceramic, quartz sand, zeolite and medical stone were used as filtering media for saline sewage treatment with proper proportion microbe, isolated from the sewage of the Wuqing sewage treatment plant. In this paper, the purification of the vertical-flow constructed wetlands (VFCWs) with different substrates was studied, and the component of the nitrogen in the influent and effluent was analyzed. The concentrations of chemical oxygen demand (COD), ammonia (NH4+ -N), total phosphorus (TP), total nitrogen (TN) and the salinity of the influent during the experimental period were 150mg•L-1, 36 mg•L-1, 8mg•L-1, 36mg•L-1 and 1.6%. Under the condition that the hydraulic loading rate was 0.25m•d-1, the average removal efficiency of COD, TP and TN were obtained about 68.81%, 32.01% and 20.72 %, respectively with Bio-ceramic; 61.92%, 31.75% and 34.33%, respectively with quartz sands; 69.47%, 35.44% and 55.28% , respectively with zeolite; and 64.77%, 32.63% and 34.72%, respectively with medical stone. This result proves that comprehensive purification of the system with zeolite is the best.

Kinetic Adsorption of Ammonium Nitrogen by Substrate Materials for Constructed Wetlands

Constructed wetlands (CWs) are engineered systems that utilize natural systems including wetland vegetations, soils, and their associated microbial assemblages to assist in treating wastewater. The kinetic adsorption of ammonium nitrogen (NH + 4-N) by CW substrate materials such as blast furnace slag (BFS), zeolite, ceramsite, vermiculite, gravel, paddy soil, red soil, and turf, was investigated using batch experiments and kinetic adsorption isotherms. Both Freundlich and Lang-muir isotherms could adequately predict the NH + 4-N adsorption process. The maximum adsorption capacities of NH + 4-N, estimated from the Langmuir isotherm, ranked as: zeolite (33 333.33 mg kg −1) > turf (29 274.01 mg kg −1) > BFS (5 000 mg kg −1) > vermiculite (3 333.33 mg kg −1) > gravel (769.23 mg kg −1) > paddy soil (588.24 mg kg −1) > red soil (555.56 mg kg −1) > ceramsite (107.53 mg kg −1). Some properties of the substrate materials, including bulk density, specific gravity, hydraulic conductivity, uniformity coefficient ( K 60), curvature coefficient ( C c), organic matter, pH, exchangeable (or active) Cu, Fe, Zn and Mn, total Cu, and Fe, Mn, Zn, Cd, Pb and Ca, had negative correlations with NH + 4-N adsorption. Other properties of the substrate materials like particle diameter values of D 10, D 30 and D 60 (the diameters of particle sizes of a substrate material at which 10%, 30% and 60%, respectively, of the particles pass through the sieve based on the accumulative frequency), cation exchange capacity (CEC), exchangeable (or active) Ca and Mg, and total K and Mg had positive correlations with NH + 4-N adsorption. In addition, active K and Na as well as the total Na had significant positive correlations with NH + 4-N adsorption. This information would be useful for selection of suitable substrate materials for CWs.

Field Application of a Renewable Constructed Wetland Substrate for Phosphorus Removal1

Rosenquist, Shawn E., W. Cully Hession, Matthew J. Eick, and David H. Vaughan, 2011. Field Application of a Renewable Constructed Wetland Substrate for Phosphorus Removal. Journal of the American Water Resources Association (JAWRA) 47(4):800-812. DOI: 10.1111/j.1752-1688.2011.00557.x Abstract: Phosphorus (P) is typically the best target to prevent eutrophication in freshwater, a biological process associated with water quality degradation. Constructed wetlands (CW) and other practices that include P removal by sorption processes in substrates can provide economical treatment of stormwater, but have limitations (e.g., large land requirements, loss of removal over time, lack of P recovery). Over the last three years, a multi-study research program addressed these limitations with a new P management concept. This concept minimizes CW size with a rejuvenation cycle (or rejuvenation) that renews P-sorption capacity in the CW substrates and enables P recovery for productive use. This study, conducted in Blacksburg, Virginia (July-September 2009), tested the efficacy of rejuvenation in the field. Methods included replicate cells of two sand substrates monitored for P removal during prerejuvenation and postrejuvenation filtration runs. One substrate contained cast iron filings as a repository for sorption capacity. Results support the following conclusions: (1) P removal is likely dependent on multiple factors including influent P concentration, previous substrate/solution equilibrium, pH, and time; (2) rejuvenation is capable of releasing P adsorbed during stormwater filtration; (3) inclusion of cast iron in substrate promotes additional P removal and enables further removal after rejuvenation; but (4) inclusion of cast iron may limit release of P during rejuvenation.

Effects of plant diversity on nutrient retention and enzyme activities in a full-scale constructed wetland

This study focused on the relationship between plant diversity (six species richness levels) and nutrient retention and enzyme activities associated with carbon, nitrogen and phosphorus cycling in a full-scale constructed wetland (CW) fed with post-treatment domestic wastewater. Effects of plant species richness on nutrient retention and enzyme activities were assessed using soil chemical and zymological methods, respectively. Retention of NH 4–N and NO 3–N in the wetland substrate increased with increasing species richness, while phosphorus retention significantly decreased under the richness level of 16 species per plot. Activities of enzymes such as dehydrogenase, β-glucosidase, invertase, phenol oxidase, l-arsparaginase, protease and nitrate reductase, while they were affected by plant species richness, were strongly depended on the presence or absence of plants in CW substrate, while activities of enzymes such as CM-cellulase, urease and acid phosphatase were strongly depended on plant species richness. We conclude that plant species richness influenced nutrient retention and enzyme activities in the substrate in our subtropical CW; increase plant species richness in CW will likely improve the efficiency of wastewater treatment.

Phosphorus removal in laboratory-scale unvegetated vertical subsurface flow constructed wetland systems using alum sludge as main substrate

This research has two eventual goals: (1) To optimize performance of subsurface constructed wetlands for removal of phosphorus (P) (2) To demonstrate that dewatered alum sludge (a by-product), can be reused as a constructed wetland substrate. To achieve these, alum sludge from a water treatment plant was characterized and used as main substrate in four experimental vertical sub-surface flow constructed wetland systems treating dairy farm wastewater. Results show that the alum sludge has suitable hydraulic characteristics (uniformity coefficient = 3.6) for use as a substrate, and in the batch studies, up to 48.6 mg-P was removed by 1 g of the alum sludge at a P concentration of 360 mg-P/l and a dosage of 5 g/l. Results from the experimental systems highlight the significant P removal ability of the alum sludge. However, the inclusion of pea gravel at the infiltrative surface of some of the systems had a negative effect on the P removal performance. Sequential P-fractionation results show that there was no significant increase in the easily extractable P, but for total P, there was significant increase, although this was found to decrease with depth. This study shows that the novel use of dewatered alum sludge can bring about high P removal in vertical subsurface flow constructed wetland systems.

Phosphorus Sorption Capacities and Physicochemical Properties of Nine Substrate Materials for Constructed Wetland

Constructed wetland (CW) is a promising technique for removal of pollutants from wastewater and agricultural runoff. The performance of a CW to remove pollutants, however, hinges on the use of suitable substrate materials. This study examined the physicochemical properties and phosphorus (P) sorption capacities of nine different CW substrate materials using both batch experiments and the Freundlich as well as the Langmuir isotherm. The nine substrate materials used in this study were turf, topsoil, gravel, midsized sand (MSS), blast furnace slag (BFS), coal burn slag (CBS), blast furnace artificial slag (BFAS), coal burn artificial slag (CBAS), and midsized artificial sand (MSAS). Experimental data showed that sorption of P increased with initial solution P concentrations for all nine substrate materials. The maximum P sorption capacity of the substrate materials estimated by Langmuir isotherm was in the following order: turf (4243 mg/kg substrate) > BFAS (2116 mg/kg substrate) > BFS (1598 mg/kg substrate) > CBS (1449 mg/kg substrate) > top soil (1396 mg/kg substrate) > CBAS (1194 mg/kg substrate) > MSAS (519 mg/kg substrate) > gravel (494 mg/kg substrate) > MSS (403 mg/kg substrate). The specific gravity of eight substrate materials (except gravel) had very significant negative correlations with the P sorption, whereas the particle diameter of D(60) and uniformity coefficient (K(60)) had positive correlations with the P sorption. The cation exchange capacity, organic matter, available ferrous, and exchangeable aluminum of the eight substrate materials also had very significant positive correlations with the P sorption, while the pH of the substrate materials showed a very significant negative correlation with the P sorption. Our study further suggests that turf and CBAS are the two relatively ideal substrate materials suitable for removal of P from a CW system.

Optimization of four kinds of constructed wetlands substrate combination treating domestic sewage

Based on the static and dynamic experiments, this paper has analyzed the adsorbing capacity for domestic wastewater pollutant (COD, NH4 +-N and TP) of four kinds of constructed wetlands substrate which were fly ash, hollow brick crumbs, coal cinder and activated carbon pellets in single and combined condition. In the static experiments, the adsorbing capacity of four substrates all grew as the adsorbing dose increased. In adsorbing COD, each substrate’s adsorbing capacity rises with the adsorbing dosage. Simultaneously, experiments show that all the adsorption of the four kinds of substrate for COD, NH4 +-N and TP follows the Freundich Rule. The dynamic experiment demonstrated that the adsorbing capacity of combined substrates is bigger than that of single substrate. Fly ash in combination with small coal cinder adsorbs COD the best, while it takes in NH4 +-N and TP the best when working with hollow brick crumbs. The combination of the two raises the removal rates up to 89% and 81% respectively. Given high cost and low adsorbing effect, activated carbon is not a suitable candidate for constructed wetlands substrate.

Phosphorus retention in the filter materials shellsand and Filtralite P ®—Batch and column experiment with synthetic P solution and secondary wastewater

Filtralite P ® and shellsand as ideal constructed wetland substrates have been tested for their P sorption capacity, both with batch and column experiments. Two columns were filled with Filtralite P ® and one column with shellsand. The shellsand (SSPS) and one of the Filtralite P ® columns (FLSP) were loaded with a synthetic P solution, while the second Filtralite P ® column (FLWW) was loaded with secondary wastewater. Ca, Mg, pH, and the P concentrations were measured in the inlet and the seven outlets along the height of the three vertical upflow columns for up to 303 days. An overall P removal rate of 92, 91, and 54% was measured in the columns SSPS, FLWW, and FLPS, respectively, for the entire experimental period. The comparison of FLWW and FLPS showed that FLWW kept its high P removal efficiency (91%) throughout the experimental period while the removal efficiency of FLPS decreased fast after reaching the 1 ppm effluent P concentration. The competition of other negative ions and the development of biofilm did not have a negative effect on P removal from wastewater. The batch experiments showed a better sorption capacity of Filtralite P ® at low initial concentrations, while for high initial concentrations the shellsand sorbed more. Shellsand had, however, a higher sorption capacity in batch experiments with used column material and high initial P concentrations. The results from both the batch and the column experiment suggest that the shellsand has a more durable P sorption capacity than the Filtralite P ® material, possibly due to the persistent high concentrations of Ca in the shellsand.

Studies on the phosphorus sorption capacity of substrates used in constructed wetland systems

Langmuir sorption isotherm was used to screen various substrates for use in removing phosphorus (P) in constructed wetlands (CW). The nine tested substrates included four sands, two soils, bentonite, and two industrial by-products of furnace slag and fly ash. Results showed that the furnace slag had the highest P sorption capacity (8.89 g P kg −1), followed was the fly ash (8.81 g P kg −1), and that of sand II was the lowest. Different kinds of sands also showed varying P sorption capacity (0.13–0.29 g P kg −1). P sorption capacity was influenced by both the physico-chemical characteristics of the substrates and the amount of organic matter (OM) added. Lifetime of sand II for P sorption estimated by Langmuir P sorption maximum was up to only 9 months in full-scale systems, while that of furnace slag could be used for up to 22 yr. Furnace slag has great potential as a CW substrate, due to its high P sorption capacity. The expected lifetime of constructed wetlands for P removal is strongly influenced by the choice of adsorbing substrate.

Characterisation of Constructed Wetland Substrates by Chemical Sequential Extraction and X-Ray Diffraction Analyses

Substrates from four-and-a-half year old constructed wetlands built to treat wastewater from an active metal mine were analysed for elevated metal and sulphur concentrations by chemical sequential extractions and X-ray diffraction analyses. Amounts of Fe, Pb, Zn and S were quantified in substrates from the first cells of multi-celled (in-series) treatment wetland systems at three different depths. The analyses showed that the majority of metals removed from the wastewater were retained in residual immobile forms in the upper 0 � /5cm of the waterlogged anaerobic substrates. Although substantial concentrations of metals and sulphur were retained in the substrates, the amounts were generally not sufficient to allow accurate mineralogical identification by X-ray diffraction. Classification of the sediments using X-ray techniques was further confounded by the highly organic nature of the wetland substrates. These results suggest that chemical analyses of wetland substrates may still provide a clearer interpretation of metal accumulation over time, especially in wastewaters characterised by relatively low metal concentrations flowing through organically rich substrates. While X-ray diffraction can provide useful interpretation of sediment crystallography and mineralogy, there are limitations in using this technology to characterise young wetland substrates.

Characterisation of Constructed Wetland Substrates by Chemical Sequential Extraction and X-Ray Diffraction Analyses

Characterisation of Constructed Wetland Substrates by Chemical Sequential Extraction and X-Ray Diffraction Analyses