Reducing Faecal Germs in Municipal Sewage Using Planted Soil Filters: Initial Results of a Pilot Plant System

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1 Reducing Faecal Germs in Municipal Sewage Using Planted Soil Filters: Initial Results of a Pilot Plant System O. Baeder-Bederski, P. Kuschk, P. Mosig and R.A. Müller UFZ Centre for Environmental Research, Leipzig-Halle, Germany M. Borneff-Lipp, M. Dürr MLU Institute for Hygiene, Martin- Luther-University Halle-Wittenberg, Germany Keywords: constructed wetlands, waste water treatment, sanitisation, faecal coliforms, filter material, Phragmites australis, irrigation water Abstract One main reason for the contamination of drinking water and food is the traditional use of untreated wastewater for irrigation purposes. The World Health Organization has therefore compiled standards governing the hygienic quality of irrigation water. However, they can only be attained if raw wastewater is adequately treated. Single-stage planted soil filters usually achieve a reduction in faecal coliform of 2 orders of magnitude. In a joint project, different types of constructed wetland systems were tested in a comparative study addressing sanitisation and other aspects of treatment performance. Initial findings from the first year s operation of a pilot plant system in Germany indicate that horizontal and vertical flow filters can achieve similar germ reduction. Filter material with a slightly higher hydraulic capacity and larger pore volume proportion impairs the sanitisation performance. There are low indications, that Phragmites australis has no direct influence on the germ reduction performance. INTRODUCTION Agriculture is the biggest water consumer, using up around 70 percent of all freshwater withdrawals worldwide (FAO 2001). With a growing world population, agriculture will face more competition from industrial and domestic water users. Given the growing world population, agriculture will face increasing competition from industrial and domestic water users. According to the director of the Food and Agriculture Organization of the United Nations: Improving the sustainable development and management of water for agriculture is essential to meet the world's growing demand for food, enhance food security and alleviate poverty. If we do not support, for example, the African countries by investing in low-cost, small-scale water-harvesting, irrigation and drainage in the poor rural communities, we will be annually pouring, as this year, hundreds of millions of dollars in food aid to avoid starvation in Africa" (Dr. Diouf, FAO Director-General, 21 March 2003, Kyoto/Japan). Hygienic concerns in the treatment of municipal sewage come to the fore when the water is to be reused or discharged into receiving streams used by humans or animals. Whenever there is a shortage of water, as is the case in arid subtropical areas of the world, waste water is traditionally used for irrigation. However, this increases the risk of epidemics, especially in developing countries, where sewage treatment is limited for financial reasons. Crops may contain pathogenic microorganisms after irrigation with raw wastewater, and the discharge of untreated sewage may contaminate drinking water resources. Therefore, the World Health Organization has compiled guidelines (WHO 1989) and instructions on employing sewage for irrigation purposes, and recommends that sewage should be treated before being used in this way (Table 1). Pond Systems Germ reduction in pond systems has been extensively examined since the 1980s (Panicker & Krishnamoorthi 1981, Polprasert et al. 1983, Pearson et al. 1987, Mills et al. 1992, and others). If we assume an average of 10 6 to 10 8 faecal coliform bacteria per 100 Proc. IC on Urban Horticulture Eds: R. Junge-Berberovic et al. Acta Hort 643, ISHS

2 ml untreated water, up to 10 5 faecal coliform bacteria per 100 ml (5 orders of magnitude) need to be removed in order to meet the WHO s irrigation guidelines. In pond technology this treatment performance can only be achieved with an extensive system of facultative and maturation ponds. One disadvantage of these systems is that the increasing area of exposed wastewater makes an ideal hatchery for insects such as mosquitoes, which can spread disease. The removal rate of faecal coliforms in pond systems consisting of anaerobic lagoons and several polishing ponds can reach 2 3 orders of magnitude under subtropical climatic conditions (Khan & Ahmad 1992). Because of the correlation between temperature and removal rates in pond systems (Marais 1974), these systems are normally used in regions with water temperatures above 12 C. Planted Soil Filters Planted soil filter systems (constructed wetlands) are also known to reduce faecal germs (e.g. faecal coliforms) in the range of 1.5 to 2.5 per treatment stage (Hagendorf et al. 2002) or 3 to 4 in multistage systems (Mitterer 1995). Constructed wetlands can be built as a subsurface system. This technology could be suitable for broad application in rural communities of developing and newly industrialized countries (Kivaisi 2001). Therefore a German-Mexican joint project with partners from universities and industry focusing on the sanitisation of domestic sewage with planted soil filters was launched in MATERIALS AND METHODS During this project, two pilot plants of a similar design were set up in Germany and Mexico. In 2001 a pilot system for 35 p. e. (population equivalents) was set up near Mexico City by the company Umweltschutz-Nord Ltd &Co. It was expressly set up for demonstration and irrigation purposes in the educational and recreational park of Fundación Xochitla A.C.. The system consists of 12 filter beds each measuring 6 m² for various wastewater treatment technologies which are charged with identical sewage. This is a major advantage compared to investigations carried out at different locations. The filters are planted with giant reed (Arundo donax) and cattail (Typha latifolia) and filled with lava material of different grain sizes. A pilot plant in Saxony (village of Langenreichenbach near Leipzig) for about 35 p.e. was set up by UFZ in the year 2000 and features a similar design to the Mexican plant (Figure 1). The comparative operation of the two systems is designed to provide findings regarding the influence of climatic factors. In contrast to the Mexican plant, additional pond systems have been included in the investigations in Langenreichenbach. As in Mexico, both planted and unplanted variants are operated. The filters in Langenreichenbach are planted with reed (Phragmites australis). Similar to the Mexican plant, the influence of two filter materials is being studied: 6 of the basins were filled with sandy material the other 6 with a mixture of expanded clay (Exclay, Fibo Exclay Ltd, Germany) and sand as filter material. During the Langenreichenbach plant s first year of operation, various loading rates were tested in order to determine the hydraulic loading which enables sufficient germ reduction at maximum throughput. After completing the loading experiments, detention studies were performed in tracer experiments. After the plant in Xochitla Park was up and running, both systems were operated under the same conditions in order to better define the climatic and other influences on the sanitisation performance between the two locations. During a second optimization phase, a combination of filter basins will be tested. The optimum variant for different combinations will then be tested in permanent operation. The experimental programme will conclude with investigations into the filter profile in order to examine the distribution of faecal indicator organisms and the general changes to the filter material after 3 years operation. Weekly water samples have been investigated both chemically and microbiologically. Chemical oxygen demand (COD) as well as biochemical oxygen demand (BOD), ammonia, nitrate, nitrite, and total nitrogen were determined by cell test 258

3 sets (WTW Ltd, Germany). Coliform bacteria as indicators of faecal contamination were cultivated on a Fluorocult LMX-Bouillon (Merck KGaA, Darmstadt, Germany) and the numbers were determined by MPN method. Other microbiological (Salmonellae, Clostridium a. o.) and parasitological parameters will be determined additionally. RESULTS The average detention time in the different systems was set at between 2 and 6 days depending on the hydraulic load used and the hydraulic design (horizontal/vertical). In order to have a sufficient stock of data to compare planted and unplanted basins, the tests with planted basins were arranged in two parallels. A reduction of 2 3 orders of faecal coliforms was measured at the pilot plant with a load of L/m 2 d. (Figures 2 and 3). Although the performance of the horizontal filters concerning the chemical oxygen demand is substantially lower, the coliform reduction of about 2.5 orders is similar to the performance of the vertical filters (Figures 4 and 5). Furthermore a difference in the reduction performance of faecal coliforms between unplanted and planted variants cannot be determined after 2 years of operation. The difference in the reduction performance between filters filled with mixed material (exclay) compared to sand probably is due to different hydraulics by the coarser grained exclay material. Even the germ reduction of the coarser grained mixed substrate filters is lower by about 1 order of magnitude. CONCLUSIONS Initial results corroborated the findings of other investigations into germ reduction in planted soil filters. Further project work should focus on systematically enhancing the germ reduction rate on both a bench and a pilot scale. From the comparative operation of different systems of planted/unplanted soil filters, the reduction of faecal coliforms observed can be summarized as follows: Comparison of the horizontal and vertical flow filters indicated that both hydraulic variants can achieve similar germ reduction. When comparing the various filter materials, one problem is that effects resulting from the surface properties of the particles and influences of the hydraulic characteristics of the entire filter could not be separated on a pilot plant scale. However, the exclay material with a large pore volume proportion had an unfavourable effect on the sanitisation performance. In a moderate climate there were indications that the inclusion of plants, especially of Phragmites australis, can have a considerable influence. Experiments using higher loads indicated only a slight negative influence. By contrast, the specific flow conditions in the filter bed appeared to have a decisive impact. In the next step the best combination and operation for multi-stage treatment plants is to be tested to reach the quality recommended for irrigation water. ACKNOWLEDGEMENTS The study is being kindly supported by the Federal Ministry for Education and Research (BMBF, Germany) and the BMBF s International Bureau for Financial Assistance (02 WA 0107 and 02 WA 0108). Literature Cited Food and Agriculture Organization of the United Nations Water and Food Security. Fact sheet, Land and Water Development Division, Hagendorf, U., Bartocha, W., Diehl, K., Feuerpfeil, I., Hummel, A., Lopez-Pila, J., Szewzyk, R Mikrobiologische Untersuchungen zur seuchenhygienischen Bewertung naturnaher Abwasserbehandlungsanlagen, Wasser Boden Luft, Heft 3, ISSN Khan, M.A., Ahmad, S.I Performance Evaluation of Pilot Waste Stabilization 259

4 Ponds in Subtropical Region, Water Science and Technology 26: Kivaisi, A. K The Potential for Constructed Wetlands for Waste water Treatment and Reuse in Developing Countries: A review. Ecological Engineering. 16: Marais, G.v.R Faecal Bacterial Kinetics in Stabilisation Ponds; Journal of Environmental Engineering Division Mills, S.W., Alabaster, G.P., Mara, D.D., Pearson, H.W., Thitai, W.N Efficiency of Faecal Bacterial Removal in Waste Stabilization Ponds in Kenya. Water Science and Technology 26: Mitterer, G Hygienisch-bakteriologische Untersuchungen an Pflanzenkläranlagen, Bundesministerium für Wissenschaft, Forschung und Kunst; Bericht aus Energie und Umweltforschung 11/95, Wien Norma Oficial Mexicana Que establece los limites maximos permisibles de contaminantes para las aguas residuales tratadas que se reusen en servicios al publico, NOM-003-ECOL-1997 Panicker, P.V.R.C., Krishnamoorthi, K.P Parasitic Egg and Cyst Reduction in Oxidation Ditches and Aerated lagoons, Journal of Water Pollution Control Federation, 53: Pearson, H.W., Mara, D.D., Mills, S.W., Smallmann, D.J Physico-chemical parameters influencing faecal bacterial survival in waste stabilisation ponds, Water Science and Technology, 19: Polprasert, G., Dissanayake, M.G., Thanh, N.C Bacterial die-off Kinetics in Waste Stabilisation Ponds, Journal of the Water Pollution Control Federation 55: World Health Organization Health Guidelines for the Use of Waste water in Agriculture and Aquacultur. Report of a WHO Scientific Group, Technical Report Series 778 ISBN , Geneva Tables Table 1. Selected standards and guidelines for the microbial quality of irrigation water Guideline/Standard Purpose Tolerance limit Faecal coliforms/100 ml World Health Organization (1989) Cat. A (raw vegetable, < 1000 restricted irrigation) World Health Organization (1989) Cat. B (cereal crops, unrestricted irrigation) no limit German Institut for Standardization Class 2 (raw vegetables.) < 200 E. coli (1999) German Institut for Standardization Class 3 (others) < 2000 E. coli (1999) Norma Oficial Mexicana (1997) direct exposure < 240 Norma Oficial Mexicana (1997) indirect exposure <

5 Figures Fig. 1. Overview and flowchart of the pilot plant in Langenreichenbach (Saxony). Photo: A. Künzelmann (UFZ). Fig. 2. Faecal coliforms (FC) content of the influent and effluent from horizontal filters (hydraulic load 40 L/m2 d, month June-August, 4 8 samples, 2 replications). Box plots indicating the 25th and the 75th percentile. The line within the box marks the 261

6 Fig. 3. Faecal coliforms (FC) content of the influent and effluent from vertical filters (hydraulic load 40 L/m2 d, month June-August, 4 8 samples, 2 replications). Box plots indicating the 25th and the 75th percentile. The line within the box marks the Fig. 4. Chemical oxygen demand (COD) in the influent and effluent of horizontal filters (hydraulic load 40 L/m2 d, month June-August, 7 18 samples). Box plots indicating the 25th and the 75th percentile. The line within the box marks the 262

7 Fig. 5. Chemical oxygen demand (COD) in the influent and effluent of vertical filters (hydraulic load 40 L/m2 d, month June-August, 7 18 samples). Box plots indicating the 25th and the 75th percentile. The line within the box marks the 263