Evaluation of two waste water treatment systems design for small pork farms and its efficiency to decrease coliforms and Salmonella spp.

A B Cordero, R G Martínez, M A Herradora and G Ramírez

Pig Production Department. Facultad de Medicina Veterinaria y Zootecnia. Universidad Nacional Autónoma de México. Circuito Exterior, Ciudad Universitaria. México D.F. 04510. México
robertomg04@hotmail.com

Abstract

The aim of this research was to design waste water treatment system and determine its efficiency to decrease total coliforms (TC) Escherichia coli, and Salmonella spp. in two different pork farms. TC, Escherichia coli and Salmonella spp., were determined and quantified in each stage of the waste water treatment system in each farm.

In each farm at least one stage of the treatment was different in bacterium concentration and at same time it was different in each phase of the treatment (P<0.05). Salmonella spp., was isolated in one farm in every stage of the treatment except in the final liquid. As conclusions: Even though the correct performance of each treatment, TC, Escherichia coli was not eliminated. The conditions of the treatments have a negative effect on the survival of Salmonella spp.

Key words: Coliforms, Enterobacteriae, filtration, liquid treatment, solid sedimentation, swine farm

Introduction

The resulting waste water in pork farms with none efficient treatment could cause the exposure of humans and animals to some pathogenic agents that represent a threat for their survival and quality of life, besides the fact that the farm could not recycle waste waters (Cortinas 2003). Some of those pathogenic agents are Total Coliforms (TC), Fecal Coliforms (FC), Escherichia coli and Salmonella spp., among others (Martínez et al 2001, Ramírez et al 2005).

The feces treatment systems are designed according to the regulations relatively to the quantity physical-chemical parameters for big farms, but for the small farms there isn´t a specific waste water treatment systems (Vanotti et al 2005). The use of fecal contamination indicating organisms instead of pathogen itself is a universal accepted principle for watchfulness and evaluation of the microbial security of water supply treatments (Madigan et al 2003).

The objective of this work was design two liquid treatments system for small pork farms and know if have an effect in the quantity of indicating organisms like: TC, Escherichia coli and Salmonella spp., so then to establish the usage of sewage recycle systems in pork farms.

Materials and methods

Farms

In order to execute this research the evaluation was carried out in two small pork farms selected in central Mexico, it was necessary to obtain certain information about each farm to define the working plan. The information about each farm will be use subsequently to interpret and discuss the results. The information was obtained by a questionnaire which was exactly the same in each farm. After that was development a waste water treatment system for each one. The specifications of the characteristics of the waste water treatment in each farm were:

Farm 1

It´s located at 2,250 meters above sea level, with warm-humid weather and rain in the summer (July to September). An average temperature of 14.8 °C (2.2 to 27.8) and an average rain of 573.3 mm annual. It has a population of 373 pigs in different ages. The water is provided by the public system, and it is used to drink, clean and wash using hosepipes. The waste water treatment consists in the fallowing operations:

a)                  A sedimentation basin (SB) of 2.34m thick, 3.06, large, and 5m depth, all the feces produced in the farm are concentrated in this sedimentation basin.

b)                 A pump of semisolids which takes the SB material into the cylindrical type solid separator (SS), so then there is separated liquid (SL) and solids.

c)                  The SL is taken to sedimentation, in two serialized pits (SP) each one is 1.66m thick, 1.95 m. large, and 2.43 m. depth. The LS is retained 48 hours in sedimentation.

d)                 The final stage of the system are three  serialized philters (Ph), which have three layers of gravel 40cm thick each one. The superficial layer is changed every three months. Each Ph is 1.5m thick, 2.5m large and 2.43m depth (Figures 1 and 2).

Farm 2

It´s located at 2,265 m above sea level, with humid weather and rain in the summer (EMM 2005). An average temperature of 14.3 °C (-1.9 to 24.5) and an average rain of 760.2 mm annual. It has a population of 560 pigs. The water is provided from wells, and it is used for animal drinking and cleaning the installations. The sewage treatment consists in the fallowing operations:

a)                  A stored cistern (SC) 3 m. thick, 5 m. large and 2 m. depth.

b)                 Three sedimentations pit (SP) 5.66 m. thick, 1.94 m. large and 1.61 m. depth.

c)                  There are 16 Ph with volcanic stone 5.66 m. by 0.80 m. by 1.60 m.

d)                 A cistern 6.29 m. large and 3.16 m. thick.

e)                  An aerator or an activated mud system (AMS) 3.5 m. high, 3 m. large and 3 m. thick, which in the bottom has a pump which applies high pressure air constantly.

Sampling

From each part of the treatment system (process) of each farm 5 one liter sample were taken. Those samples were measured temperature and pH using a potentiometer. For the measuring process sterile containers were used, and in the case of flow samples letting flow a 10 volume quantity more than the quantity of the sample. And in the case of gutters and basins a sampled container was hold by a string.

In order to carry out the identification of Salmonella spp., it was necessary to have concentrated sewage water, which was obtained using a Moore hyssop for 24 h in the sampling area. After the 24 h the hyssop was removed and placed in the transfer medium Cary Blair transport (BD, BBL, cat.211102), the samples were placed in sterile plastic bags. All the samples were processed in the bacteriological diagnosis laboratory of the Pig Production Department, Faculty of Veterinarian Medicine, in the Universidad Nacional Autonoma de Mexico.

Determination of total coliforms (TC) and Escherichia coli

For the identification and quantification of TC, FC, and Escherichia coli., the multi-tube fermentation technique was used to determine the more probable number (MPN) and IMVIC test (Niemi et al 2005).

Identification of Salmonella

The identification of Salmonella was carried out by using the Analytical Profile Index 20E (API 20 E) (Biomeriux, cat. 20100) (Arias et al 2003).

Statistical analysis

Because the data of MPN of TC and E.coli didn’t show a normal distribution even after being converted with a base 10 logarithm, the Kruskal-Wallis test was done in order to see if there was any difference among different stages of treatment in each system of each farm, in the case that difference exists the Wilcoxon test was applied in order to know in each system which stage of the treatment was different, everything according to JMP8.0 program (2008). The efficiency of elimination of TC, Escherichia coli, and Salmonella spp., was observed respectively by percentages.

Results and discussion

The MPN/100 ml was the same for TC and Escherichia coli in each system. As for the count of TC and Escherichia coli, it showed the same quantity and is because all the effluent in pork farms is formed mainly by excrement, which agrees with the reported by Chinivasagam et al (2004).

In this research bacterium presence was found in raw liquids that come to the sedimentation basin of 1.58 x 10¹⁰ to 1.94x10¹¹  MPN/100ml; other authors have reported quantities of coliforms and Escherichia coli of 1.0x10⁶  to 2.1x10⁸ UFC/100ml (Chinivasagam et al 2004) and 2.6x10⁶ UFC/g (García et al 2005).

In each farm there is significant statistical evidence that at least one of the stages of the treatment is different as regards concentration of bacterium (MPN of TC and Escherichia coli) (P<0.01) (Table1).

As for the efficiency of removal of coliforms bacterium it is showed in table 2.  It is noticed that the percentages of removal are high in the final liquid in all farms.

The use of a solid-liquid separator is important in the treatment of pork effluents because it helps to the removal of abundant solids in this kind of effluents. According to the results its efficiency was almost the same 99.6%.

The percentage of efficiency of the removal of bacterium in the sedimentation pits was similar in the two systems. In connection with the process of sedimentation in this research, the quantities of coliforms and Escherichia coli found are similar to others authors reports, as 9.0x10⁶ UFC/g (García 2005) and 3.9x10⁵ UFC/g (Ramirez et al 2005). Thus we can say that the efficiency of sedimentators achieves similar parameters ranks, but the difference consists in the characteristics of the raw liquids that enter into the system.

It is reported that the filtering process preceded by an efficiently sedimentation process showed a significant impact in the removal of bacterium, virus, and other microorganisms because using both it is eliminated up to 95% of these agents (Davis 1991; Pepper et al 1996) which is not consistent with the finds of farm two (75%). It is important to say that this kind of process do not depend totally on the quantity of filters, the most important was the design inside the system but above all to standardize the optimum time of hydraulic retention in the filters which agree with different authors (Pepper et al 1996; Environment Protection Agency 2000). The great number of filters in farm two originated an increased in the transit of the liquid.

The aeration process implemented in farm two there wasn´t efficiency of removal bacterium, on the contrary it seems to be an increase of 18.14 %, because in the activated mud process there is generation of biomass (Vanotti et al 2007).

It is possible to conclude that the processes used in each system reduce the quantity of bacterium, with the exception of the aerator of farm two. These results do not agree with García et al (2005), those authors concludes that the primary system of treatment based on separation and sedimentation do not reduce the quantity of coliforms in any of the stages, what differs from the results of this research.

Identification of Salmonella spp.

Both farms had a previous diagnosis of Salmonella spp. The percentage of isolation of Salmonella spp., are showed in table 3 in each stage of the treatment of each system, in which it is observed that only in farm 1 the isolation of Salmonella spp., was not achieved, while in farm two the incoming raw liquid has among 60% (farm 2).

As for the identification of Salmonella spp., the fact that it was not found in the final results of the treatment´s process in farms where it had being identified before in the affluent do not agree with García (2005) and Ramírez et al (2005) who have isolated Salmonella enterica (serovar choleraesuis) in the sedimentation basin, in separated liquid, and in the sedimentation pit. However, Chinivasagam et al (2004) pointed out that after the treatment only four (23%) were positive to Salmonella spp., from 13 positive farms. Thus there is a negative effect in the bacterium during the treatment, the decrease in the percentage of isolation after the treatment could be connected with the adverse circumstances for the bacterium in the system and the principal negative effect could be the increase of temperature in the stock sewage water, as Arrus et al (2006) reported.

As a conclusion it could be said that in general the operations of each system fulfill its function independently, but there are factors that affect the efficiency. Because of the microbiological characteristics of the pork effluents it is necessary to implement a process of disinfection, not only in order to comply with regulations but in order to recycle the effluents.

Acknowledgements

The authors appreciate the support of PAPITT  IN223903.

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Received 15 January 2010; Accepted 20 April 2010; Published 10 June 2010

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