COMPARISON OF AGRONOMIC QUALITY OF EFFLUENT ... - BVSDE

Seminario Internacional sobre Métodos Naturales para el Tratamiento de Aguas Residuales

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 25157 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, ToC, 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

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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 23oC 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.

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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

AP FP UASB FP DP

Real Real Real Pilot Pilot

Flow m3/d 864 1726 864 11.5 11.5

HRT days 2.0 7.0 0.3 20 20

Length M 52 112 9.55 67.8 67.8

Width m 26 52 7.2 5.1 5.3/4.7*

Depth m 4.0 1.5 4.3 0.7 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 2003. 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-PO4), 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

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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 Ginebraa Parameter pH Temperature (°C) Alkalinity (mg CaCO3/l) CODt (mg/l) CODf (mg/l) BOD5 (mg/l) TSS (mg/l) TKN (mg/l) P-Org (mg/l)

N

Average / range

Standard deviation

50 50 10 27 18 14 25 5 5

6.60 – 7.09 24.0 – 27.0 185 526 202 342 225 42.3 5.1

0.2 0.8 10.0 62.9 35.7 39.4 46.9 17.1 2.6

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 pH Temperature (°C) SAR Electric Conductivity (dS/m) TKN (mg/l) N-NH3 (mg/l) N-NO3 (mg/l) P-Total (mg/l) P-PO4 (mg/l)

n

Mean

60 60 12 60 12 12 12 12 12

6.8 26.5 3.3 0.6 30.1 18.8 0.04 8.6 6.6

Max-Min 7.1-6.5 28.6-22.4 4-2.5 0.7-0.5 44.7-18.8 28.2-11.8 0.1-0.01 13.6-5.9 10.9-3.0

Standard deviation 1.74 0.60 0.06 7.13 4.61 0.03 2.60 2.32

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

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Table 4. Agronomic effluent quality from study technologies (n: 12) Parameter EC SAR TKN P-Total

Technology

Mean (dS/m or mg/l)

Max-Min (dS/m or mg/l)

0.56 0.58 0.60 2.7 2.9 2.8 20.28 23.45 25.71 7.44 7.67 7.69

0.63-0.52 0.66-0.52 0.64-057 3.2-2.2 3.4-2.5 3.1-2.5 30.5-14.8 29.3-19.1 35.1-19.7 12.3-4.3 12.5-3.1 12.7-5.3

Pilot FP Pilot DP Full FP Pilot FP Pilot DP Full FP Pilot FP Pilot DP Full FP Pilot FP Pilot DP Full FP

Standard deviation 0.03 0.05 0.02 0.3 0.25 0.18 4.96 3.07 4.00 2.65 3.02 2.39

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)

0.7 0.6 0.5 0.4 1

8

15

22

29 36 43 51 Time (days)

R WW Pilot DP EC FAO ds/m

63

70

77

84

Pilot FP Full FP

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

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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

3 2 1 0 1

8

15

SAR RW

22

29 36 43 51 Time (days)

SAR Pilot FP

63

SAR Pilot D P

70

77

84

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