Livestock Research for Rural Development 24 (2) 2012 Guide for preparation of papers LRRD Newsletter

Citation of this paper

Treating pig wastewater by applying a model of fish pond or biodigester tank followed by a fish pond in Phuoc Tho state farm

Luu Huu Manh, Nguyen Nhut Xuan Dung, Bui Thi Le Minh and Mai Thuy Duong

College of Agriculture and Applied Biology, Cantho University, Vietnam
lhmanh@ctu.edu.vn

Abstract

Two methods of  treating the wastewater from pig farms (by draining directly into a fish pond or through a biodigester and subsequently a fish pond) were evaluated with two levels of pigs/surface water area. Measurements were made of temperature, pH, dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), suspended solids (SS), total nitrogen, total phosphorus, total Coliforms and parasite eggs. 

The model of biodigester followed by the fish pond was the more effective and the quality of the wastewater in the fish pond met the government standards (type A Vietnam Standard: TCVN 5945 – 2005). The standards were not met by treating the wastewater only with the fish pond.

Key words: BO, Coliforms, DO, parasite eggs, pH, pig manure, Vietnamese Standard


Introduction

Pig production is one of the most important livestock sections in agriculture in the Mekong delta.  Intensive pig farms and small scale farms have grown remarkably; in most cases,  pig waste is directly drained to the water surfaces, resulting in severe environmental pollution. Realizing that problem, some waste bio-treatment methods have been applied to reduce environmental pollution by using fish ponds or fish ponds followed by water hyacinth ponds (Luu Huu Manh et al 2009).

The aim of this study was to evaluate the effects of two wastewater treatment models:  fish pond alone or biodigester followed by fish pond; and numbers of pigs per unit of surface water in the fish pond. Biochemical parameters were compared against the Vietnamese government standard (TCVN 5945 – 2005).


Materials and Methods

The study was conducted with two models in the Phuoc Tho state farm.

Model 1: Treating pig waste by using fish pond

Model 1 consisted of two fish ponds with water surface of 600 and 1400m2. Pig numbers were 2.35 and 9.12 heads/100m2 water surface (Table 1).


Table 1. Number of pigs per unit of water surface area (fish pond)

Treatment

Pig numbers

Fish pond surface area (m2)*

Pigs/100m2 water surface area

FP-H

32

600

5.33

FP-L

33

1400

2.36

*Fish species:  Tilapia; Snakeskin gouram; common carp. Density:30 fish/m2.  

Figure 1. Sample collection points (1and 2) in model 1.

Model 2: Treating pig waste by biodigester tank in combination with fish pond

In the second model, pig waste was treated in a biodigester tank before going to the fish pond; this model consisted of two different treatments, pig numbers per 100m2 water surface area were 9.12 and 5.4 heads (Table 2).


Table 2. Number of pigs per unit of volume (biodigester tank) and unit of water surface area (fish pond*)

Treatment

Pig number (heads)

biodigester tank volume (m3)

Fish pond surface area (m2)

Pig number/m3 biodigester

Pig number/100m2 water surface area

BDFP-H

985

50

10800

19.7

9.12

BDFP-L

227

50

4200

4.54

5.4

Fish species: Tilapia, Snakeskin gouram and common carp. Density: 30 fish/m2


Figure 2. Sample collection points (3, 4 and 5) in model of biodigester in combination with fish pond

 

Sample collection

Samples were collected from 06:00 to 09:00 in the morning after cleaning the pig pens. The washings from the pen, consisting of faeces, urine and leftover feed, were discharged, piped and drained into a fish pond (Model 1) or a biodigester tank (Model 2). There were 5 selected sample points (Figures 1 and 2). The first and third points were at the end of the pipe where the flow of wastewater went into the fish pond and biodigester tank.  The second and fifth points were in the fish ponds and the fourth was in the biodigester tank. Samples collected included three replications. Total number of the samples was 78. They were held in plastic bottles, previously cleaned by washing in non-ionic detergent, rinsed with tap-water and finally with non-ionic water.  During sampling, the bottles were rinsed with the sample wastewater and then filled from a depth of 20 to 30cm below the level of the wastewater. To determine total Coliforms, samples were stored in sterile bottle. Bottles were labeled, transported to the laboratory and stored at 4C prior to analysis.

Analytical methods

Suspended solids (SS) were determined gravimetrically after oven drying at 105C (APHA 1995). Total nitrogen (Ntot) was determined using Kjeldahl digestion. Total phosphorus (Ptot) was determined by using a colorimetric ascorbic-molybdate method after sample digestion with a H2SO4/H2O2 mixture (Murphy and Riley 1962). For chemical oxygen demand (COD) and five-day biological oxygen demand (BOD5), samples were stored at 20C and analysed by Winker’s method (APHA 1995). DO was also determined using the Winkler method. Temperature and pH were as determined using a pH meter (Hanna instrument).

Total Coliforms were determined using the Most Probable Number method (APHA 1998). The isolation and identification of parasitic eggs were done by the methods of Fiilleborn (1920) and Benedek (1940). Evaluation of the water quality was based on Vietnamese Standard (TCVN 5945-2005) according to the Environmental Law (ASEAN-10) (1998).

 Statistical analysis

Data were subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) available in Minitab 13.2. The Tukey test in the same software was used to detect significant differences among treatment means. 


Results and Discussion

Effect of treating pig waste by fish pond

The temperature in the wastewater collected in the pig pen (Table 3) was lower (28.3C) than that of the fish pond (29.9C). This increased temperature in the fish pond could be from absorbing the sunlight and from the oxidation of organic matter. The pH of the fish ponds (6.9 and 6.7) was reduced as compared to the sample collected from the pig pen (7.4). The reduction of pH was perhaps cause by carbon dioxide from respiratory processes of aquatic animals and oxidation of growing organic matter occurring in the fish pond. However, these parameters were less than type A of Vietnamese Standard TCVN 5945-2005.

Dissolved oxygen (DO) in the pig pen wastewater was not observed, while it was 1.43 and 3.14 mg/litre for the two different pig densities in the fish pond. The DO concentration in fish pond increased because of the diffusing of oxygen from the air by activities of the Tilapia and common carps, which prefer floating feeds and flocks of fish often swim on surface of the water.

In the pig pen, five-day biochemical oxygen demand (BOD5) for treatments FP-H and FP-L were very high (957and 877mg/litre, respectively); both were significantly reduced (72.5 and 72.7 mg/litre) in the fish pond, but this parameter exceeded type A of Vietnam Standard TCVN 5942-2005.

Chemical oxygen demand (COD) and suspended solids (SS) were reduced significantly by around 94% after wastewater went to the fish pond. Nevertheless, the values exceeded the type A (TCVN 5942-2005). This could be the result of the organic matter in the waste  going into the fish pond being used as a feed source for the fish. In addition, organic matter deposited on the bottom of the fish pond would be disintegrated by microorganisms.

Total nitrogen (Ntot) was reduced more than 84% through the fish pond and was below type A of Vietnamese Standard TCVN 5942-2005.  Similarly, total phosphorus (Ptot) in models 1 and 2 was also reduced rapidly from 330 and 296 mg/litre to 41.9 mg/litre (approximate 87% and 91%, respectively). However, Ptot exceeded the type A of Vietnam Standard TCVN 5942-2005. If fish pond wastewater, which contains a high level of total phosphorus, is discharged directly into rivers it would cause eutrophication and be toxic  for aquatic animals.

Parasitic eggs were not found in the fish pond; this indicated that the fish pond was effective in controlling this component in the pig faeces.

Total Coliforms in fish pond were high (1.1x106 MPN/100ml) and exceeded type A of Vietnamese Standard TCVN 5942-2005. The presence of Coliform bacteria indicates that the water has been contaminated with human or animal feces and is a potential hazard for the community.  


Table 3. Effect of the fish pond treatment in model 1

Pigs/100 m2 water surface

Collection points of samples

P

TCVN 5945-2005

A

 

Pig pen

Fish pond

Temperature, oC

FP-H

28.3

29.9

>0.05

40

FP-L

28.7

29.8

>0.05

pH

FP-H

7.4

6.7

>0.05

6 - 9

FP-L

7.4

6.9

>0.05

DO, mg/litre

FP-H

0.00

1.4

 

 

FP-L

0.00

3.1

 

BOD5, mg/litre

FP-H

958a

72.5b

<0.05

30

FP-L

877a

72.7b

<0.05

COD, mg/litre

FP-H

1650a

98.7b

<0.05

50

FP-L

1287a

72.7b

<0.05

SS, mg/litre

FP-H

1350a

117b

<0.01

50

FP-L

1350a

88.3b

<0.01

Ntot, mg/litre

FP-H

54.4a

8.5b

<0.05

15

FP-L

50.5a

7.8b

<0.05

Ptot, mg/litre

FP-H

330a

41.9b

<0.05

4

FP-L

296a

25.4b

<0.05

Parasites, egg/litre

FP-H

9.00

0.00

 

 

FP-L

12.00

0.00

 

Total Coliforms, MPN/100ml

FP-H

 

1.1x106

 

3x103

2.35

 

4.6x105

 

a,b,c Data in a row with different letters differ at P < 0.05 or P < 0.01. 

Effect of treating pig waste by biodigester in combination with fish pond

The temperature in the biodigester tank was higher than in the pig pen and fish pond and probably caused by oxidation of organic matter. The temperature was similar to the optimum temperature for the anaerobic disintegration process of 30-35C recommended by Bitton (1999). This parameter in the fish pond was less than type A of Vietnamese Standard TCVN 5945-2005. The pH in the biodigester was slightly reduced because of the acids and gases resulting from anaerobic digestion organic matter. This parameter was within the range of the type A Vietnamese Standard TCVN 5942-2005. DO was not found in the wastewater of the pig pen and biodigester tank. However, in the fish pond, it was 3.43 mg/litre in treatment BGFP-H and was 3.48 mg/litre in treatment BGFP-L. The increase of DO could be from the photosynthesis process of aquatic plants and diffusion  of oxygen from the air.

Generally, BOD5, COD and SS were reduced up to 72%, 77% and 74%, respectively through the biodigester tank, but exceeded the type A standard (TCVN 1945-2005) , while in the  fish pond, these parameters were reduced more than 97% and were less than the type A of Vietnamese Standard TCVN 5942-2005. In principle, COD reflects the amount of organic matter oxygenated by chemical factors and BOD5 the amount of organic matter oxygenated by biological factors. wastewater could be treated by biological effectively methods if the ratio of BOD5/COD is equal or more than 0.05 (Tran Van Nhan et al 2002). In this study, the ratio of BOD5/COD was 0.55 and 0.57 in the two different treatments and thus could be subjected successfully to application of biological treatment methods.

Total nitrogen in the biodigester tank varied between 11.3 and 23.7mg/litre in treatments BGFP-H and BGFP-L. In the fish pond, it was reduced by 89.5% (treatment BGFP-H) and 92.0% (treatment BGFP-L) and was within the type A standard (TCVN 1945-2005). Total phosphorus in the wastewater from the pig pen was reduced through the fish pond (by 98.5 and 98.6% in treatments BGFP-H and BGFP-L, respectively). However, it exceeded the standard type A (TCVN 1945-2005). 

Parasite eggs were not found in the biodigester tank nor in the fish pond. Total Coliforms in the fish pond were 2.4x103 and 2.6x103 MPN/100ml in the two treatments and exceeded the standard type A (TCVN 1945-2005).  


Table 4. Effect of the treatment method of biodigester followed by a fish pond

Treat

Collection points of samples

P

TCVN 5945 – 2005 A

Pigpen

biodigester

Fish pond

Temperature, oC

 BGFP-H

29.67a

31.0b

28.4c

<0.05

40

 BGFP-L

29.33a

31.3b

28.5c

<0.05

pH

 BGFP-H

7.47a

6.4b

7.08a

<0.05

6 - 9

 BGFP-L

7.23a

6.6b

7.05a

<0.05

DO, mg/litre

 BGFP-H

0.00

0.00

3.43

 

 

 BGFP-L

0.00

0.00

3.48

 

BOD5, mg/litre

 BGFP-H

1172a

327b

28.7c

<0.01

30

 BGFP-L

1156a

96.0b

24.0c

<0.01

COD, mg/litre

 BGFP-H

2120a

486b

47.2c

<0.01

50

 BGFP-L

2043a

186b

42.3c

<0.01

SS, mg/litre

 BGFP-H

1833a

473b

48.3c

<0.01

50

 BGFP-L

1750a

180b

43.0c

<0.01

Ntot, mg/litre

 BGFP-H

63.48a

23.7b

6.69c

<0.01

15

 BGFP-L

56.25a

11.3b

4.632c

<0.01

Ptot, mg/litre

 BGFP-H

386.90a

109b

6.01c

<0.01

4

 BGFP-L

439.10a

91.3b

5.96c

<0.01

Parasites, egg/litre

 BGFP-H

9.00

0.00

0.00

 

 

 BGFP-L

11.00

0.00

0.00

 

Total Coliforms, MPN/100mlitre

 BGFP-H

 

 

2.6x103

 

3x103

 BGFP-L

 

 

2.4x103

 

 BGFP-H: 19.7 pigs/m3 biodigester tank volume and 9.12 pigs/100m2 water surface area.
 BGFP-L: 4.5 pigs/m3 biodigester tank volume and 5.4 pigs/100m2 water surface area.
a,b,c
Data in a row with different letters differ at P < 0.05 or P < 0.01.


Conclusions


References

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Received 12 November 2011; Accepted 4 January 2012; Published 7 February 2012

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