Assignment- Worldwide review of various substrates used in constructed wetlands

Worldwide review of various substrates used in constructed wetlands

Introduction

There are several types of substrates, including soil, sand, gravel, zeolite, limestone, plastic and ceramics etc. It is suggested to collect the substrate materials near the construction location (MEP, 2011). Different region has its own waste removal requirement for particular types of pollutants. Researchers now are trying to find new substrate materials to gain the efficiency to remove different types of pollutants for different kind of CWs. A combination of different substrate materials is also an attempt.

Various Substrates

Soil, sand and gravel are the main three types of substrate materials existed and widely used in constructed wetlands. Recently, many other materials were developed to structure the constructed wetlands as the substrate.

Aiming to reduce the water eutrophication occurring by excessive phosphorus to a particular low level required by EPA of USA, researchers designed vertical up-flow columns with wollastonite as the substrate to test the efficiency of reducing phosphorus in secondary wastewater (Brooks et al., 2000). The research result was excellent. The vertical flow columns with wollastonite showed efficiency to remove soluble phosphorus. Wollastonite showed a promise of being an economic means for the constructed wetland.

For testing different substrate media in the vertical flow constructed wetlands, researchers from Greece reported their research result (Stefanakis & Tsihrintzis, 2009). In the research, Stefanakis and Tsihrintzis designed five small-scale, cylindrical vertical flow constructed wetlands to test the simulated Greece wastewater. The treatment group contained four kinds of substrates, including carbonate rock, igneous rock, zeolite and bauxite. All four materials gained satisfying removal rate of organic matter and nitrogen. But the phosphorus removal rate was lower. Although zeolite and bauxite substrates gained higher nitrogen removal rate and higher phosphorus respectively, the removal rates were not significantly higher than carbonate and igneous rock substrates gained.

Chinese researcher also gained results. Four researchers studied the performance of two substrates made of coke and gravel to reduce Zn, Cu and Pb which are heavy metals (Chen et al., 2009). Although the study was aiming to exam whether the real removal results of these three heavy metals fitted the prediction of the first order dynamic model, these removal results were still able to claim the efficiencies of coke for Zn, Cu and Pb. The Pb removal efficiency is 95-99%. At the same time, the coke substrate constructed wetland only provided an efficiency of 54-91% for both Zn and Cu. It is difficult to claim that coke substrate is more efficient than the gravel substrate from this study.

Wang and Zhang (2012) studied the performance and comparison of bamboo splint and palm silk as the substrate materials for the stable surface flow wetland. The control group is a combination of gravel, cinder, ceramist and sand. The alternative part of Bamboo Splint Group was the additional 10-centimeter-thick bamboo material and 5-centimeter-thick sand filter bed. The alternative part of Palm Silk Group was the additional 10-centimeter-thick palm silk material. The test parameters were COD, TP and TN. The results of removal efficiencies of each kind of pollutants were remarkable.

Removal Rate of Sewage Water with SSFW
	COD	TP	TN
Bamboo Splint	73.97%	61.42%	28.98%
Palm Silk	78.37%	69.42%	24.40%
Control group	66.61%	58.71%	22.23%

Wang & Zhang, 2012

Other materials have also been tested the suitability of applying as the substrate materials. Oyster Shell could significantly adsorb phosphorus in a vertical subsurface flow constructed wetland (Wang et al., 2013). Xin (2013) studied 32 articles and commented on the wood mulch substrate that it was efficient for N removal in a vertical flow constructed wetland. He also agreed that the organic substrate in a HSSF constructed wetland would give a rise of P chemical element (Xin, 2013).

Other than natural materials, industrial materials could also be applied as the substrate. Plastic can be used as the substrate, but the results of removal performance were not better gravel (Burgoon et al, 1989).

Conclusion

Various substrate materials other than soil, sand and gravel were tested and developed. Most of these materials could bring better removal efficiencies than the common materials. The combination of common materials and new substrate materials also showed good pollutant removal performance.

Reference

Ministry of Environmental Protection. (2011). Technical specification of constructed wetlands for wastewater treatment engineering. Ministry of Environmental Protection of the People’s Republic of China. pp3.

Brooks. A, Rozenwald. M, Geohring. L. Lion, L. and Steenhuis, T. (2000). Phosphorus removal by wollastonite: A constructed wetland substrate. Ecological Engineering 15 (2000) 121–132. Available at: http://soilandwater.bee.cornell.edu/publications/BrooksEE00.pdf [Accessed date: May 5^th, 2016]

Stefanakis, A. and Tsihrintzis, V. (2009). Comparison of Various Substrate Media on the Performance of Vertical Flow Constructed Wetlands. The 11^th International Conference on Environmental Science and Technology. Available at: http://www.academia.edu/1095226/Comparison_of_various_substrate_media_on_the_performance_of_Vertical_Flow_Constructed_Wetlands [Accessed date: May 5^th, 2016]

Chen, M. Tang, Y. Li, X. and Yu, Z. (2009). Study on the Heavy Metals Removal Efficiencies of Constructed Wetlands with Different Substrates. J. Water Resource and Protection, 2009, 1, pp: 1-57. Available at: http://file.scirp.org/pdf/JWARP20090100004_45816707.pdf [Accessed date: May 5^th, 2016]

Wang, C. and Zhang, J. (2012). Study on Different Substrates in Stable Surface Flow Wetland. Ecosystem & Ecography. Available at: http://www.omicsonline.org/study-on-different-substrates-in-stable-surface-flow-wetland-2157-7625.1000109.pdf [Accessed date: May 5^th, 2016]

Wang, Z. Dong, J. Liu, L. Zhu, G. Liu, C. (2013). Study of oyster shell as a potential substrate for constructed wetlands. Water Science and Technology: Water Supply. Volume 13, Issue 4, pp 1007-1015.

Xing, A. (2012). Recent Development in wetland technology for wastewater treatment. Halmstad University. Available at: http://www.diva-portal.se/smash/get/diva2:571109/FULLTEXT01.pdf [Accessed date: May 5^th, 2016]

Burgoon, P. Reddy, K. and DeBusk, T. (1989). Domestic wastewater treatment using emergent plants cultured in gravel and plastic substrates. Constructed wetlands for wastewater treatment. Lewis Publishers Inc., pp. 536–541. Available at: https://soils.ifas.ufl.edu/wetlands/publications/PDF-articles/138.Domestic%20wastewater%20treatment%20using.pdf [Accessed date: May 5^th, 2016]