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Recycling of Wastewater from Pig Farms in Urban and Peri-Urban Agriculture
Supamard Panichsakpatana
Kasetsart University
Chatuchak, Bangkok 10900
Thailand, 2007-06-01

Abstract

Urbanization is the main cause of change in cropping pattern in the central part of Thailand. In provinces where farmlands occupy more than 15% of the total land area, such as Bangkok and Samut Prakarn, land use is changing from rice paddy to ornamental plants and vegetables. Meanwhile, in areas where agricultural land exceeds 50% of the total land area, like Chachoensao and Nakhon Pathom, most farmlands are planted to vegetables and fruits other than rice. In peri-urban areas, the main agricultural activities are livestock production and aquaculture. Most of the livestock in these areas are monogastric, particularly pig and poultry, since they are not roughage dependent and are more efficient in feed conversion. The serious problems in this case are the wastes and wastewater from farmlands and their contamination of nitrate and salinity to the surface and the ground water. This paper discusses some technologies in the management of wastewater as fertilizer and fertigation. Wastewater could replace as much as 80-100% of the application rate of chemical fertilizers depending on the type of crop. For example, it could replace up to 100% of the chemical fertilizers at the recommended rate of chemical N for corn, sweetcorn, Guinea grass (Panicum maximum Jacq), sugarcane, and cassava at 62.5, 93.75, 156, 93.75, and 112.5 kg N.ha-1, respectively. Better yield and nutrients of the crops were generally observed in the combination treatment of a half dose of the chemical N + wastewater. In vegetable, such as Chinese green mustard [Brassica campestris ssp chinensis var parachinensis (Bailey)] and/or Pak-choy (Brassica campestris var chinensis), application of the wastewater could give 80-100% as much yield as those treated with chemical N. The application of concentrate wastewater could replace some amount of water consumption of the crops. For instance, wastewater at the above recommended rate could replace irrigation water as much as 220,000-440,000, 187,500-375,000 and 380,000-760,000 liters.ha-1 in one season of corn, Chinese green mustard and sugar cane, respectively. Fertigation of the crops could be done for the whole season by mixing the wastewater with irrigation water to reach a concentration of about 100 mgN.L-1. At these recommended rates, there was no evidence of nitrate contamination in the ground water. There was also no evidence of zinc and copper accumulation in the tested crops and in the soils although the treated soils were very sandy in texture and the ground water level was shallow. There were high amounts of coliform bacteria (540,000 MPN.100 ml-1) and E. Coli (1.2 x 103 CFU.ml-1) in the wastewater. Hookworms and threadworms (Strongyloides stercoralis) were found in both soils treated and untreated with the wastewater but they were not found in the treated crops.

Key words: wastewater, urban and peri-urban agriculture, nitrate contamination, fertigation, pig farm, water pollution

Recent Changes in Cropping Pattern and Livestock Production

Urban Agriculture

The number of big cities with populations of over 1 million have been increasing rapidly during the last decades and has resulted in increased food production in these areas. With this phenomenon, great impacts on natural resources, especially on land and water, have occurred. According to the UN World Water Development Report, water quality is declining in most global regions. The problem is more obvious in urban and peri-urban areas where half of the world population will be living by 2007. By 2030, towns and cities will have risen to nearly two-thirds, resulting in drastic increases in water demand in these areas.

When rural areas transform into towns, agricultural patterns also gradually change into urban and peri-urban agriculture (UPA). Rice field decreases in proportion with the population density. The land is used more for mixed cropping instead of rice monoculture. High-value cropping such as ornamentals is replacing rice cultivation. Vegetable fields and orchards are replacing rice fields as well. For example, in the Bangkok plain during the period 1989-1995, vegetable areas increased by more than 35%, fruit trees increased by about 20%, whereas paddy lands decreased by 2.7% and sugarcane by 3.4% (Saridnirun and Pages 1999). The effect of urbanization on farmlands is illustrated in Table 1(998) and Table 2(1149) and Fig. 1(1197). Bangkok and its vicinity is comprised of seven provinces. Bangkok and Samut Prakarn are the most crowded areas. Population density in these areas exceeds 1,000 persons.km -2 ( Table 2(1149)), such that farm land occupies no more than 15% of the total land areas. These provinces' agricultural fields are mostly planted to ornamentals and vegetables ( Table 3(1191)). In areas where agricultural land exceeds 50% like Chachoengsao and Nakhon Pathom, most of the farmlands are planted to vegetables and orchards side by side with rice field.

Peri-Urban Agriculture

In urban agriculture, excess of nutrients (especially N and P) are considerably less since nutrient loss occurs by way of discarding agricultural wastes. In fact, many portions of wastes are recycled through various means. For example, vegetable wastes are used as animal feeds while some are used for composting. However, much more nutrients are imported into the system. For example, in vegetable production covering 2,500 ha, an amount of 250, 250 and 300 t.year -1 of nutrients N, P 2O 5, and K 2O, respectively, in the form of chemical fertilizers are imported into the system. Besides chemical fertilizers, however, 3,000 t of duck waste, 500 t of peanut residue, and over 1,000 t of farm compost are also incorporated into crop production (Duangngam and Pages 2000). By the loss of these nutrients, the ground and the surface waters in the area might be contaminated with N, P, and the pesticides used in vegetable production.

In peri-urban agriculture, the situation is different. The main agricultural activities in peri-urban areas are livestock production and aquaculture. Most of the livestock in these areas are monogastric especially pig and poultry since they are not roughage dependents and are more efficient in feed conversion. To profit from economies of scale and to be near the market for their perishable products, the new pig and poultry production system is often based on large industrialized units close to urban agglomerations. These units often have not enough knowledge to manage livestock wastes on their own farm. It therefore has to be discharged directly to water courses or is lost through nonexisting or insufficient handling facilities (leaching, runoff, overflow of lagoons etc.) which pollutes the environment. The more serious problems in this case are the wastes and the wastewater from farmland and their contamination of nitrate and salinity to the surface and the ground water.

UPA such as aquaculture and livestock production produces large amounts of wastewater that becomes major sources of water contamination since livestock excretes 70-90% of the nutrient N, P, K and heavy metals taken up in the feed. For instance, Thachin River which is less than 50 km from Bangkok, an affluent tributary of Chao Phraya River, was ranked the most polluted river in Thailand from the year 2000-2002. This was caused by the wastewaters from pig farms and industrial plants.

Wastewater Management in Urban and Peri-Urban Agriculture

Wastewater from Stationary Ponds

The author conducted experiments to investigate wastewater management in Chol Buri and Rayong provinces located around 100-150 km east of Bangkok. The sites were situated in Bang Pakong River Basin where the production of pig, poultry, and fish accounted for 25%, 32%, and 58% of the total production in Thailand, respectively (Panichsakpatana 2003). Since the area is under the export promotion program by the Thai Government, it can be expected that pig production will rise sharply and may reach two-folds of the present figure in the next 10 years. At present, excessive livestock populations result to overloads of N (264%), P (413%), and K (279%) in some districts of the region. The contamination of wastewater in Bang Pakong River has already occurred in some regions. Since Cu and Zn are used as food additives for pigs, the two elements could have been contaminating the soil and the river as well (Harada et al., 1993).

The soil in PK farm in Chol Buri province was Sathon series (Stn): fine-loamy, mixed, semiactive, isohyperthermic Typic Plinthaquults. The soil in NR farm in Rayong province was classified as Chalong, coarse loamy variant (Chl-co): coarse-loamy, kaolinitic, iso-hyperthermic Typic Kandiudults.

The wastewater from the PK farm was from pregnant sows, whereas that from the NR farm was from the fatteners. The analyses of the wastewater used in this trial were as follows:

  • Total N NH 4-N NO 3-N
  • (mg.L -1)
  • PK farm 209-385 (297) 165-230 (189) 0-3.5 (2)
  • NR farm 175-385 (228) 150-210 (180) 0-4.2 (2)

The figures in the parentheses are the average values for the corresponding items. With the estimation from the mean values, the wastewater from the pregnant sows contained 65% inorganic-N, whereas that from the fatteners contained inorganic-N as much as 80% of the total-N.

Five kinds of crops were chosen for the field experiments, namely, corn, sugarcane, Chinese green mustard [ Brassica campestris ssp chinensis var parachinensis (Bailey)], (CGM), oil palm, and cassava. Corn, sugarcane, and Chinese green mustard were planted in PK farm, whereas, oil palm and cassava were planted in NR farm.

All the experiments except that of oil palm were conducted in Randomized Complete Block Design (RCBD) with four replications. There were six treatments for testing of corn and sugar cane and five treatments for Chinese green mustard. The treatments were as follows:

  • T1 : No chemical fertilizer, no wastewater
  • T2 : Nitrogen fertilizer
  • T3 : Chemical fertilizer, N-P-K
  • T4 : Wastewater, low rate, WWL: (using Total-N for calculation with T2 rate)
  • T5 : Wastewater, high rate, WWH: (double rate of T4)
  • T6 : Wastewater + Chemical fertilizer (T4 + 1/2T3)

The N rate used in T2 and the chemical rate in T3 were the rates recommended by the Department of Agricultural Extension, Ministry of Agriculture and Cooperatives. There was no sole treatment of nitrogen fertilizer in the experiment of Chinese green mustard.

Experiments in Pregnant Sow Farm

Nitrogen mineralization of wastewater in the soils. The laboratory experiment was conducted to test N mineralization of the waste water. Urea was used as the standard treatment. It was found that the wastewater showed its benefit better than urea ( Fig. 2(1101)). The NH 4-N from the wastewater was available immediately after applying it to the soil, whereas, no available N was observed at the day of urea application (67.2 vs 33.6 mg N.kg -1). Nitrification in the soil receiving the wastewater occurred after three days of applying the wastewater. At the later period, mineralization of urea and the wastewater appeared in the same manner as its rate and magnitude. The wastewater supplied nitrogen to the soil more or less at the same amount and as fast as the urea did. Regardless of its harmful effects, it could be used as a liquid fertilizer in this case.

Efficiency of wastewater as fertilizer for crops. The rates of chemical fertilizers and wastewater are shown in Table 4(1026). There was no N-fertilizer treatment in the CGM experiment. In the wastewater treatments, calculation of the application rates was based on the rate of N-fertilizer and the total N content in the wastewater. It was then designed as the wastewater at low rate (WWL) since the total N could give inorganic N of only 65-80% according to the previous analytical results. The rate of wastewater in the WWH treatment was 2 x WWL since the fertilizer application in the recommended rate was still low for the optimum growth of the crops.

The effects of wastewater and chemical fertilizer on crop yields were clearly observed in the corn experiment ( Table 5(1146)). With the application of chemical fertilizer, either N alone or N-P-K, the plants produce significantly higher yields than those grown with no treatment. Application of wastewater at low rate was found to enhance the corn yield slightly. When the plants received wastewater at a higher rate, the yield was significantly higher than those grown in the control plot. With a combination of chemical fertilizer and wastewater, seed yield was as much as 1,109 kg.rai-1 compared to 744 kg.rai -1 of those with no fertilizer and wastewater application. There was no significant difference in yield among the fertilizer treatment and the wastewater treatment.

In the vegetable experiment, the yield of Chinese green mustard was 24.7 kg in the control plot ( Table 5(1146)). With wastewater application, the plant yield significantly increased to 32-33 kg. The figures might not be statistically different but it would give additional income to farmers in the sense that more value could be obtained from the increased yield with less wastewater to be managed. With chemical N-P-K application, the plant yield could reach 39 kg. In other words, wastewater enhanced the plant growth and yield as effectively as 82-84% of the chemical fertilizer at the treated rates.

Since the land for planting sugarcane has been applied with fertilizers before, the effect of the treatments on cane yield was not clearly observed in the first planting season. Regardless of the statistical difference, application of the wastewater could increase sugarcane yield as much as 0.7-1 t/rai (4.3-6.3 t/ha). Application of less chemical fertilizer together with the wastewater, could get a yield increase of as much as nearly 3 t/rai (18.8 t/ha). Better response of the crop to the wastewater is expected in the next ratooning season.

Experiments in the Fatteners Farm

The wastewater from pig farms could be used as nutrient source for oil palms. It releases inorganic N at the same time and amount as that of urea. It could replace chemical fertilizer as much as 0.5-0.3-0.9 kg N-P 2O 5-K 2O.plant -1year -1. With this rate of application, the oil palm in the wastewater treated plots could uptake the plant nutrients such as N, P, K, Mg, Cu, and Zn the same amount as those in the chemical fertilizer treated ones. Furthermore, the oil palm could produce its oil content as high as when it received the chemical fertilizer ( Table 6(1092)).

The wastewater supplied nutrients for cassava awas s much as the chemical N-P-K at the rate of 18-7.5-7.5 kg, N-P 2O 5-K 2O.rai -1. The advantage of the wastewater was that it could produce starch slightly higher than the chemical fertilizer could. With a combination of the wastewater and the chemical fertilizer, the above ground portion of cassava became very healthy compared to the control ( Table 7(1018)).

Contamination of No3, Cu, ZN and Human Pathogen

In order to analyze NO 3-N, ground water was collected a week after every application of the wastewater in the experimental fields. In tracing the harmful effects of Cu and Zn, the wastewater, the soils, and the crops were collected and analyzed. The results showed that there was no nitrate contamination in the ground water at the application rate of the wastewater ( Fig. 3(1192)). The contents of Cu, Zn, and NO 3-N in the crops treated with the wastewater were not higher than those treated with the chemical fertilizers. There were high amounts of coliform bacteria (540,000 MPN.100 mL-1) and (1.2 x 10 3 CFU.mL-1) in the wastewater. Human parasites were not found in the wastewater and in Chinese green mustard. The hookworms and the threadworms ( Strongyloides stercoralis) were found in both soils treated and untreated with wastewater.

Wastewater from Biogas Production

Biogas production from animal wastes is quite common in temperate countries since it can be used to produce heat or electricity during winter. In tropical countries like Thailand, not so many animal farms adopt biogas production. This might be because of the high cost of biogas plant. Normally, the effluent from biogas production (EFB) contains fewer nutrients than the wastewater from the stationary ponds. In the author's experiments, the chemical properties (in average) were pH 7.5, EC 1.6 mS.cm -1, BOD 23 mg.L -1. The contents of total N, total P, total K, total Mg, total Ca, total Na, total Zn, and total Cu were 68-98, 21, 50, 23, 20, 60, 0.1, and 0.1 mgN.L -1, respectively. Judging from its chemical properties and nutrient contents, EFB could be the good source of N and K for crop production.

The EFB could produce crop yield equivalent to 156 and 93.75 kg N.ha -1 of chemical fertilizer for Guinea grass and sweetcorn, respectively ( Fig. 4(1023) and Table 8(1098)). In the case of vegetable, the yield of Pak-choy in EFB plot was equivalent to 85% of that in the (125 kg N.ha -1) CF plot, whereas ½ EFB + ½ CF could produce crop yield comparable to that produced by the CF. ( Fig. 5(1051)).

Wastewater As Fertilizer and Irrigation Water

In pig production areas, wastewater from pig farms is the main source of water pollution. Bang Pakong river near Chol Buri (CBR) province and Tachin river near Kamphaeng Saen (KPS) district are heavily polluted with the wastewater from the pig farms. In order to reduce the BOD in the wastewater, many pig farms in Kamphaeng Saen, Nakhon Pathom province produce biogas from the wastewater. The effluent from the biogas production contained total N in the range of 68-98 mg N.L -1 with BOD of 25 mg.L -1. With the low content of nitrogen in the wastewater of the biogas case, wastewater could substitute irrigation water for the whole planting period of Guinea grass and vegetable (Pak-choy, Brassica campestris var chinensis) whereas it could replace irrigation water by as much as 175,000 L.ha -1.week -1 in planting sweet corn, or 1,225,000 L.ha -1 in one growing season ( Table 9(1170)).

The wastewater from the stationary ponds contained total N higher than that from the EFB. Its concentration was in the range of 175-385 mgN.L -1 (with the average of 228 and 297 mgN.L -1). With high N content in the wastewater, the amount of wastewater applied for corn and vegetable was about one third of that from biogas production applied for the corresponding crops.

Based on the results of these experiments, it could be recommended that fertigation could be done for the whole season of the crops by mixing the wastewater with irrigation water to have a concentration of about 100 mgN.L -1.

Conclusion

The wastewater from pig farms contained a lot of NO 3-N and NH 4-N. About 60-80% of nitrogen in the wastewater was in inorganic forms. The wastewater could replace chemical fertilizers by as much as 80-100% of the application rate depending on type of growing crops. It could replace up to 100% of the chemical fertilizers at the recommended rate of the chemical N for corn, sweet corn, sugar cane, oil palm, and cassava. The same results might be observed from the grass crops. Better yield and nutrients of the crops were generally observed in the combination treatment of the half dose of chemical N + wastewater. In vegetable, such as Chinese green mustard and/or Pak-choy, application of wastewater could give 80-100% as much yield as those treated with chemical N.

Wastewater could replace some amount of water consumption of the crops. For instance, wastewater at the above recommended rate could replace irrigation water as much as 220,000-440,000, 187,500-375,000 and 380,000- 760,000 L.ha -1 in one season of corn, Chinese green mustard and sugar cane, respectively. If the wastewater contained total N no higher than 100 mgN.L -1, it could replace irrigation water for the whole season in some crops. One appropriate method for mitigation of water pollution from livestock effluents is to use it as fertilizer and irrigation water. The wastewater should be collected in the lagoons and it should be mixed with irrigation water before applying it to the crop fields at a concentration of about 100 mgN.L -1 if the wastewater would be used for the whole growing season.

Acknowledgment

This project was financially supported by the Food and Agriculture Organization (FAO). The author expresses his sincere appreciation for the kind assistance and support of FAO Regional Office for Asia and the Pacific, Thailand; and the Livestock, Environment and Development Initiative (LEAD), Animal Production and Health Division, FAO, Rome. The strong support from the Department of Livestock Development, Ministry of Agriculture and Cooperatives is also gratefully acknowledged.

References

  • Chunnasit, B., J. Pages and O. Duangngam. 2000. Incident of Bangkok city development on peri-urban agricultural patterns and cropping systems evolution. In Proc. on The Chao Phraya Delta: Historical Development, Dynamics and Challenges of Thailand's Rice Bowl. Kasetsart University, Bangkok.
  • Duangngam, O. and J. Pages. 2000. Nutrient recycling: an overview of Bangkok peri-urban agricultural sector, an example of recycling technology: the Agrifiltre process. In Mini-symposium on Nutrient Recycling for Peri-urban Agriculture. Kasetsart University, Bangkok.
  • Harada, Y., K. Haga, T. Osada and M. Koshino. 1993. Quality of compost produced from animal wastes. JARQ 26: 238-246.
  • Ministry of Agriculture and Cooperative. 1998. Data Statistic Ministry of Agriculture and Cooperative.
  • Panichsakpatana, S. 1995a. Utilization of effluent from biogas production as nitrogen source for Guinea grass (Panicum maximum Jacq.) grown on Kamphaeng Saen soil. Kasetsart J. (Nat. Sci.) 29: 182-192.
  • Panichsakpatana, S. 1995b. Efficiency of some selected organic wastes as nitrogen source for sweet corn grown on Kamphaen Saen soil. Kasetsart J. (Nat. Sci.) 29: 358-370.
  • Panichsakpatana, S. 1995c. Utilization of effluent from biogas production as nitrogen source for Pak-choy (Brassica campestris var chinensis) grown on Kamphaeng Saen soil. Kasetsart J. (Nat. Sci.) 29: 445-453.
  • Panichsakpatana, S. 2003. Fertigation of some selected crops with wastewater from pig farms: an appropriate method for mitigation of water pollution from livestock effluents, pp 89-90. In the First Southeast Asia Water Forum. SEAWF, IWMI, FAO, Chiang Mai.

Index of Images

Figure 1 Relationship between Population Density and Farmland Ratio.

Figure 1 Relationship between Population Density and Farmland Ratio.

Figure 2 N-Mineralization of Wastewater in PK Farm.

Figure 2 N-Mineralization of Wastewater in PK Farm.

Figure 3 Ec and the Contents of Ammonium and Nitrate in Ground Water.

Figure 3 Ec and the Contents of Ammonium and Nitrate in Ground Water.

Figure 4 Yield of Guinea Grass.

Figure 4 Yield of Guinea Grass.

Figure 5 Yield of Pak-Choy (Brassica Campestris Var Chinensis).

Figure 5 Yield of Pak-Choy (Brassica Campestris Var Chinensis).

Table 1 Land Use in Urban Agriculture

Table 1 Land Use in Urban Agriculture

Table 2 Population Density in Bangkok and Vicinity

Table 2 Population Density in Bangkok and Vicinity

Table 3 Comparative Crop Area at Provincial Level (1998)

Table 3 Comparative Crop Area at Provincial Level (1998)

Table 4 Fertilizer Rates (KGN.Rai-1) Used in the Experiments

Table 4 Fertilizer Rates (KGN.Rai-1) Used in the Experiments

Table 5 Yield of Crops Growing in PK Farm in Chol Buri (2002)

Table 5 Yield of Crops Growing in PK Farm in Chol Buri (2002)

Table 6 Yield of Oil Palm (GM.Plant-1)

Table 6 Yield of Oil Palm (GM.Plant-1)

Table 7 Growth and Yield of Cassava

Table 7 Growth and Yield of Cassava

Table 8 Ear Size and Sugar Content of Sweet Corn

Table 8 Ear Size and Sugar Content of Sweet Corn

Table 9 Amount of Wastewater Used in One Season of the Crops (X1,000 L.Ha-1)

Table 9 Amount of Wastewater Used in One Season of the Crops (X1,000 L.Ha-1)

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