COMPARISON OF AGRONOMIC QUALITY OF EFFLUENT FROM CONVENTIONAL AND DUCKWEED WASTE STABILISATION PONDS FOR REUSE IN IRRIGATION

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1 COMPARISON OF AGRONOMIC QUALITY OF EFFLUENT FROM CONVENTIONAL AND DUCKWEED WASTE STABILISATION PONDS FOR REUSE IN IRRIGATION Madera, C.A.,* Van der Steen N.P.** and Gijzen H.J.** * Instituto CINARA, Univalle. AA Cali., Colombia ** UNESCO-IHE, Institute for Water Education, P.O.Box 3015 DA Delft, Netherlands. ABSTRACT This paper discusses the comparison of agronomic quality of effluent from conventional and duckweed waste stabilisation pond for reuse in irrigation. The research was carry out in Ginebra Research and Transfer Station (GRTS), located in Ginebra municipality, small town in southwest of Colombia. Effluent from three technologies were compared, Upflow Anaerobic sludge Blanket (UASB) + pilot Duckweed pond (PDP)(1); UASB + Pilot Facultative pond (PFP) (2); and Full-scale Anaerobic + Facultative pond (FFP) (3). Weekly samples were taken from raw wastewater and effluents of mentioned technologies to determinate EC, SAR, ph, T o C, N and P. The results show that there are no significant differences in agronomic effluents quality between all technologies. According to FAO (1985) the effluent is classified slightly to moderate restrictions on use in irrigation from SAR quality and infiltration rate problem in the soil can occur in the future. Based of the criteria of USA agriculture department (1954), the water is classified in group A, indicating low alkali and salinity hazard and the water can be used in irrigation of all kind of crops. The nutrients (N and P) contents in the effluents are higher than sugarcane (main crop in Ginebra and Valle del Cauca) demand and problems such as yield reduction and leaf burn may occur. KEY WORDS Duckweed, effluents, irrigation, reuse, stabilisation ponds, sugar cane, wastewater. INTRODUCTION The accelerated population growth, especially in developing countries, contamination of both surface and groundwater, uneven distribution of water resources and periodic droughts have forced water agencies to search for innovative sources of water supply (Asano, 1991). Wastewater is converted in extra source for water demand and reuse of wastewater has been indirectly recycled through human history. This phenomenon became even more common with the development of sewerage and urbanization process. The current reuse of wastewater for agricultural purposes is attractive to many local authorities but especially to those in water-scarce regions. Wastewater is reused for different purposes in many parts of the world and it has contributed to the development of regulations aimed to protect both the environment and public health (Asano and Levine, 1996). Most of the researchers have concentrated on microbiological wastewater quality, however, the agronomic parameters are also important. Salinity, dissolved solids, sodium absorption ratio play a very important role when reuse projects are planed. The soil properties can deteriorate and yield is cut down due to the presence of these substances. Is well known that natural system for wastewater treatments are among the best technology to meet the WHO (1989) guidelines for irrigation purpose, but there is a little information about to meet FAO (1985) guidelines. Stabilisation ponds, duckweed ponds, land treatment, and wetlands are examples of this group. In this paper we present the results obtained from a study on the comparison of agronomic effluent quality from duckweed and stabilization ponds to irrigate sugar cane in Valle del Cauca, Colombia. MATERIALS AND METHODS The research was carried out at the Ginebra Research and Transfer Station on Wastewater Treatment and Reuse (GRTS) located in Ginebra town, Valle del Cauca region in Southwest Universidad del Valle/Instituto Cinara Madera, C.A. et al 222

2 Colombia. This station is run under a co-operative agreement between Universidad del Valle/Institute Cinara and the regional Water and Sewerage Company, ACUAVALLE S.A, E.S.P. Ginebra is a small municipality with a population of 8,000 inhabitants located towards the centre of the Valle del Cauca region, as shown in Figure 1.The average temperature throughout the year is 23 o C and the main economic activity is growing sugar cane and grapes. The rainfall is 1,189 mm/year. The coverage of water supply and sewerage (combined system) services are 100% and 98% respectively. Additionally, there is a Wastewater Stabilization Pond (WSP) system to treat the municipal wastewater. ACUAVALLE S.A. E.S.P. manages these public services. Cali? Figure 1. General location of study area in Ginebra and view of technologies The study was focussed on the effluents of the following technologies: (1) Anaerobic + facultative ponds (full-scale, standard technology), (2)real scale UASB + pilot scale duckweed pond (DP); and (3) real scale UASB + pilot scale facultative pond (FP). Table 1 displays the main characteristics of these systems for the operating conditions during the research. Figure 1 shows the mentioned technologies. Table 1. Main characteristics of the technologies under investigation System Scale Flow HRT Length Width Depth m 3 /d days M m m AP Real FP Real UASB Real FP Pilot DP Pilot /4.7* 0.7 This channel pond has a trapezoidal shape. First number is surface width and second bottom width HRT: Hydraulic Retention Times. The experimental phase was conducted during November 2002 to January Weekly (Wednesday) samples were grabbed at the influent and effluent of each technology. The samples were composite samples obtained during a five hour period (9:00 a.m to 1:00 p.m.). Temperature, ph and electric conductivity (EC) were measured in the field. The following analyses were performed in the laboratory: Total Kjeldahl Nitrogen (TKN), Nitrate-N, Ammonium-N, Total-P, Phosphate (P-PO 4 ), Calcium (Ca), Magnesium (Mg), Sodium (Na) according to Standard Methods (APHA, 1992). To assess the performance of the technologies the data was analysed by descriptive statistics (i.e. variation ranges, arithmetic averages, standard deviations). Correlation between different variables Universidad del Valle/Instituto Cinara Madera, C.A. et al 223

3 was analysed and behaviour of different parameters with time was compared. The Excel 2000 (Microsoft Corporation) package was used to carry out all statistical analyses of data and graphs. A one-factor ANOVA analysis allowed testing to comparing between performances of technologies with a confidence level of 95 percent. The F distribution was applied for this purpose as described in the literature (Kvanli et al., 2000). RESULTS AND DISCUSSION Table 2 displays the average composition of the domestic wastewater of the Ginebra town (Peña, 2002). The strength of the wastewater of Ginebra town is slightly higher than that of an average domestic wastewater (Metcalf and Eddy, 1991). Table 2. Wastewater composition at Ginebra a Parameter N Average / range Standard deviation ph Temperature ( C) Alkalinity (mg CaCO 3 /l) COD t (mg/l) COD f (mg/l) BOD 5 (mg/l) TSS (mg/l) TKN (mg/l) P-Org (mg/l) t, total; f, filtered. a: Source (Peña, 2002) Table 3 shows the characteristics for agronomic quality of raw wastewater during the research. The values for all parameters are similar to the data presented in Table 2, which indicates that raw wastewater composition is rather constant during the last few years. Table 3. Raw wastewater characteristics during the study at Ginebra Parameter n Mean Max-Min ph Standard deviation Temperature ( C) SAR Electric Conductivity (ds/m) TKN (mg/l) N-NH 3 (mg/l) N-NO 3 (mg/l) P-Total (mg/l) P-PO 4 (mg/l) SAR: Sodium Absorption Ratio The effluents agronomic quality was measured by salinity (EC ds/m), SAR, Sodium Ion concentration and nutrient concentrations, such as nitrogen and phosphorus. Salinity and SAR are the principal parameters for evaluation of potential soil and crop problems when using effluent for irrigation. Table 4 shows the effluent quality from the technologies under investigation. Universidad del Valle/Instituto Cinara Madera, C.A. et al 224

4 Table 4. Agronomic effluent quality from study technologies (n: 12) Parameter Technology Mean (ds/m or mg/l) Max-Min (ds/m or mg/l) Standard deviation EC Pilot FP Pilot DP Full FP SAR Pilot FP Pilot DP Full FP TKN Pilot FP Pilot DP Full FP P-Total Pilot FP Pilot DP Full FP Salinity in the Effluents from all technologies was low (average mean between 0.56 to 0.6 ds/m) and were classified according to FAO (1985) as none restriction on use. The raw wastewater can also be classified in the same category. Figure 2 shows the variation of salinity during the study. The removal of salts was lower in all technologies, which indicates that the pond capacity for salts elimination is low. This in accordance with some reports that state that natural and conventional systems cannot remove salts (Patterson, 2001). The salt concentration in a few cases is higher in the effluents from all technologies than in the raw wastewater. This may be due to accumulation of salts in the ponds as a result of water losses might be by evaporation. However, in DP is it cannot correlate to evaporation losses, because the plant is a barrier for sunlight. The sugar cane yield will not be affected, because the effluent EC value is lower than 1.7 ds/m, the critical value for reduced production of this crop (Aguas et al., 2002). 0.8 EC (ds/m) Time (days) R WW Pilot FP Pilot DP Full FP EC FAO ds/m Figure 2. Effluent EC Variations during the Study. The SAR mean value fluctuated between 2.7 and 2.9 (Figure 3) and was similar for all technologies and effluents is located in the second range for infiltration evaluation according to FAO guidelines. With SAR value 2.7 (average) and EC 0.60 (ds/m) value (average) the water is classified slight to moderate restriction on use, because infiltration rates in the soil can be affected (FAO, 1985). The sodium effluent concentration fluctuated between 41 and 59 mg/l for PFP; 40 and 58 mg/l for PDP; Universidad del Valle/Instituto Cinara Madera, C.A. et al 225

5 and 48 and 56 mg/l for FFP. Sodium in all technologies was less than 3 meq/l. The effluents are classified none degree of restriction on use, with regard to the sodium ion concentration (FAO, 1985). 5 4 SAR Time (days) SAR RW SAR Pilot FP SAR Pilot D P SAR Full FP Figure 3. Effluents SAR variations along the Study The mean ratio sodium/ calcium was 2.1:1, 2.6:1 and 2.3:1 for PFP, PDP and FFP, respectively. In DP the value was very close to the critical value (3:1) and soil dispersion and structural breakdown may possibly occur due to excess of sodium in the effluent and in addition significant infiltration problems may also arise. The concentration of TKN in the effluents was lower than in raw wastewater. The removal efficiency in each technology was 29 % FP, 18% DP and 11 % full-scale. The pilot FP reaches the best performance, but statistically all effluents has similar concentration. The ammonia removal efficiency was 0, 3, and 21 %, for full FP, PDP and PFP, respectively. There is a large difference between pilot FP and the other technologies. The removal efficiencies of total-p were 17, 15 and 14 % (p<0.05) for PFP, PDP and FFP, in this order. There is not statistical differences between technologies from the removal of P-total point of view. In order to test the performance of technologies for removal of agronomic parameters, the ANOVA test was carry out to analyse the data from effluents. The null hypothesis was that the two pilot technologies produce the same agronomic effluent quality. For comparison with the full-scale technology, the hypothesis was that the full-scale technology produces effluent with better agronomic quality.* Table 5 is the anova table for testing the hypothesis. Comparison of the calculated variance ratio (F- Value) for three technologies and twelve examples for each technology, with conservative critical value of the F-distribution for degrees of freedom v1=1 and v2=23, suggest that the null hypothesis should be accepted. Universidad del Valle/Instituto Cinara Madera, C.A. et al 226

6 Table 5. Summary of ANOVA for Agronomic Quality Parameters EC SAR TKN P-Total Technologies compared F-value F-critical p α Decision rule Pilots DP and FP Accept H o Pilot DP and FFP Accept H o Pilot FP and FFP Rejected H o Pilots DP and FP Accept H o Pilot DP and FFP Accept H o Pilot PFP and FFP Accept H o Pilots DP and FP Accept H o Pilot DP and Full FP Accept H o Pilot FP and Full FP Rejected H o Pilots DP and FP Accept H o Pilot DP and Full FP Accept H o Pilot FP and Full FP Accept H o The ANOVA test shows that DP and FP s have similar performance, produce the same agronomic effluent quality, since null hypothesis was accepted. There is a difference between the pilot and full scale FP s, since ANOVA rejects the null hypothesis for TKN and EC. This indicated that the HRT and deep of pond can be a factors for salts removal The Full technology arithmetic mean for EC is high than Pilot FP, which may be due to higher water losses in the full scale pond as compared to the pilot pond, because full pond has higher surface area than pilot unit. The guidelines of the USA Agriculture Department (ADUSA) (1954) classify the effluents from GRTS in a different category than FAO (1985) with respect to potential infiltration problems. FAO mentioned that at the prevailing SAR values infiltration rate problems in soil might occur. In contradiction, ADUSA indicates that no problems can be expected with this water quality if it is used for irrigation, the effluent is classified as group A. Mara (2003) mentioned that most of the effluents from WSP are located in group A or B, according to ADUSA guidelines. The best performance in removal of N was achieved in Pilot FP, with 29% for TKN and 21% for ammonia, although the ANOVA test shows that there is no statistic difference of the performance between pilots technologies for these parameters. Only the differences between the pilot and full scale facultative ponds are significant. This may indicate that the retention time, water column deep, temperature and ph are a factor for N removal in this kind of ponds and this is confirmed by various authors in literature (Mara, 1997, Korner and Vermaat, 1998; Zimmo 2003). FAO guidelines (1985) classify the water based on its nitrogen content as slight to moderate restriction on use, because the N concentration in the effluents are between 5-30 mg/l, the range for mentioned category. This classification is because too much nitrogen can reduce the crop yields or cause crop damage such as leaf burn. Phosphorus removal by P-Total was low as compared to the literature (Mara, 1997). The efficiency were 17, 15 and 14% for Pilots FP, DP and full FP, respectively. The lower value due to the fact part of the phosphorus was taken up by algae and may be remained in the pond effluent. Other reason in SP algae settled in the bottom of pond and phosphorus could be released again into the water column, as mentioned by Mara (1997). In duckweed uptake of P was weak and may be biofilm attached to walls and sediment can be absorbed part of P has more importance in P losses. The load of N in effluent (average 280 kg/ha-y) is higher as compared to the suggested load value to sugar cane 100 to 250 kg/ha-y (Cenicaña 2002) and FAO (1985) recommended 200 kg/ha-y. Universidad del Valle/Instituto Cinara Madera, C.A. et al 227

7 Yields as well as product quality may be adversely affected by excess of N application. Sugarcane is sensible. The problem might be that water demand and nitrogen demand are not in parallel. In the sugarcane case, additional difficulties may arise because N applications are three times during the growth period only (Quintero, 1997). CONCLUSIONS 1. The technologies produce effluent with similar agronomic quality and the effluent can be used for sugar cane irrigation. 2. Effluent from Pilot DP does not have statistical differences for SAR and EC parameters compared to both facultative ponds. There is a difference between pilot scale and full scale facultative ponds for EC according to the ANOVA test, indicating that HRT and area are factors for salts removal. 3. From EC and SAR parameters, there are some contradictions in the classification of the effluents, because regarding on FAO (1985) water has restriction (slightly to moderate ) and from USA agriculture department (1954) water is classified in group A, signifying low alkali and salinity hazards and therefore the water can be used for all kind of crops. 4. The technologies produce effluents with similar TKN and total-p concentration and no statistical significant differences were observed between Pilot DP and both facultative ponds. There is a difference between pilot and full scale facultative ponds, indicating that HRT, depth, temperature and ph are factors that affecting nutrient losses mechanism. The effluents from technologies are classified as slightly to moderate restriction on use for nitrogen parameter according to FAO (1985). ACKNOWLEDGMENTS The authors would like to thank the Cinara Institute, the UNIVALLE-UNESCO-IHE alliance and ACUAVALLE S.A, E.S.P for the financial support and laboratory work. REFERENCES. Aguas, J.; Jimenez, H.R. and Peña, J. (2002). Uso de la Agricultura de Precision para Identificar la Tolerancia de la Caña de Azucar a Sales y Sodio. Cenicaña, carta trimestral. Año 24, numero 2. Cali, Colombia. Asano, T. (1991). Planning and Implementation of Water Reuse Projects. Wat. Sci. Tech., 24(9), Asano, T. and Levine, A. (1996). Wastewater Reclamation, Recycling and Reuse: Past, Present and Future. Wat. Sci. Tech., 33(10-11), Cenicaña. (2002). Carta Trimestral. Año 24, Numero 2. Colombia. FAO. (1985). Water Quality for Agriculture. Irrigation and Drainage Technical Paper No 29. Rome, Italy. Korner, S. and Vermaat, J.E. (1998). The Relative Importance of Lemmna Gibba L, Bacteria and Algae for the Nitrogen and Phosphorus Removal in Duckweed-Covered Domestic Wastewater. Wat Res., 32(12), Kvanli, A.; Pavur, R.J. and Guynes, S. (2000). Introduction to Business Statistics. 5 th ed. South- Western College publishing. Cincinnati USA. Mara, D. (1997). Waste Stabilisation Ponds. Design Manual for Waste Stabilisation Ponds in India. Lagoon technology international. Leeds.UK. Mara, D.D. (2003). Domestic Wastewater Treatment in Developing Countries. London: Earthscan ltd (in press). Universidad del Valle/Instituto Cinara Madera, C.A. et al 228

8 Metcalf and Eddy, Inc. (1991). Wastewater Engineering Treatment, Disposal and Reuse. 3 rd edn, McGraw Hill Inc, New York. Patterson, R.A. (2001). Wastewater Quality Relationships with Reuse Options. Wat Scie Tech., 43(10), Peña, M.R. (2002). Advance Primary Treatment of Domestic Wastewater in Tropical Countries. Develop of High Rate Anaerobic Ponds. PhD thesis, University of Leeds, UK. Quintero, R. (1997). Fertilizacion Nitrogenda de la Caña de Azucar. Cenicaña. Cali, Colombia. United State Department of Agriculture (1954). Diagnosis and Improvements of Saline and Alkali Soils. Agriculture handbook No 60, United States Department of Agriculture, Washington, D.C. WHO. (1989). Guidelines for the Safe Use of Wastewater and Excreta in Agriculture and Aquaculture.Geneva. World Health Organization. Zimmo, O. (2003). Nitrogen Transformation and Removal Mechanisms in Algal and Duckweed Waste stabilisation Ponds. PhD Thesis. IHE, Delft, Netherlands. Universidad del Valle/Instituto Cinara Madera, C.A. et al 229