Disposal and Treatment Methods for Pesticide Containing Wastewaters: Critical Review and Comparative Analysis

Mariam T. Al Hattab, Abdel E. Ghaly

Department of Process Engineering and Applied Sciences, Faculty of Engineering, Dalhousie University, Halifax, Canada.
Department of Process Engineering and Applied Sciences, Faculty of Engineering, Dalhousie University, Halifax, Canada..

DOI: 10.4236/jep.2012.35054                

Abstract

Pesticides provide the primary means for controlling organisms that compete with man for food and fibre or cause injury to man, livestock and crops. They played a vital role in the economic production of wide ranges of vegetable, fruit, cereal, forage, fibre and oil crops which now constitute a large part of successful agricultural industry in many countries. After application to the target areas, pesticide residues are removed from applicators by rinsing with water which results in the formation of a toxic wastewater that represents a disposal problem for many farmers. Pesticides can adversely affect people, pets, livestock and wildlife in addition to the pests they are intended to destroy. The phenomenon of biomagnification of some pesticides has resulted in reproductive failure of some fish species and egg shell thinning of birds such as peregrine falcons, sparrow hawk and eagle owls. Pesticide toxicity to humans include skin and eye irritation and skin cancer. Therefore, care must be exercised in the application, disposal and treatment of pesticides. Currently, disposal of pesticide wastewater is carried out by: 1) land cultivation, 2) dumping in soil pits, plastic pits and concrete pits or on land and in extreme cases in streams near the rinsing operation, 3) use of evaporation beds and 4) land filling. These methods of disposal are unsafe as the surface run off will reach streams, rivers and lakes and the infiltration of the wastewater into the local soil will eventually reach ground water. The treatment methods currently used for pesticide wastewater include: 1) incineration (incinerators and open burning), 2) chemical treatments (O3/UV, hydrolysis, Fenton oxidation and KPEG), 3) physical treatments (inorganic, organic absorbents and activated carbon) and 4) biological treatments (composting, bioaugmentation and phytoremediation). Therefore, the choice of safe, on farm disposal techniques for agricultural pesticides is very important. A comparative analysis was performed on 18 methods of pesticide disposal/treatment using six criteria: containment, detoxification ability, cost, time, suitability for on farm use, size and evaporation efficiency. The results indicated that of the 18 methods evaluated, 9 scored above 80/100 and can be used on farm. They were organic absorbents (97), composting (94), bioaugmentation (92), inorganic absorbents (90), Fenton oxidation (86), O3/UV (83), activated carbon (82), hydrolysis (82), and land cultivation (80). The other methods are not suitable for on farm use as they suffered from containment problems, high cost and variability of effectiveness.

Keywords

Pesticides; Health; Soil; Water; Disposal; Treatment; Land Cultivation; Disposal Pits; Evaporation Ponds; Landfills; Incineration; O3/UV; Fenton Oxidation; Hydrolysis; Bioremediation; Bioaugmentaion

1. Introduction

Pesticides provide the primary means for controlling organisms that compete with man for food and fibre or cause injury to man, livestock and crops. They are classified based on the pest they control as shown in Table 1. Pesticide expenditures account for 13% - 22% of total costs of production per hector. The worldwide pesticide consumption and expenditures in 2007 (Table 2) were 2.37 billion kg and 39.4 billion dollars, respectively [1]. Table 3 illustrates the top 10 countries applying higher rates (kg/hectare) of pesticides [2]. Ten companies (Table 4) account for 87.2% of the total sales [3].

Pesticides played a vital role in the economic production of wide ranges of vegetable, fruit, cereal, forage, fibre and oil crops which now constitute a large part of successful agricultural industry in many countries. They lower crop losses, increase revenue to farmers from the additional marketable yield obtained with their use and thus lower the cost of production per unit output [4]. Other benefits include: 1) reduced uncertainty of crop loss from pests, 2) increased profit to farm input suppliers (machinery, fertilizer, chemicals and seed companies) from increased sale, 3) benefit to consumers through decreased price of raw foods or improved quality of food products and 4) benefit to society as whole (farmers, consumers, farm suppliers, food processors) from increased employment opportunities and expanded export

Table 1. Common types of pesticides.

Table 2. 2007 worldwide consumption and expenditures of pesticide active ingredients [1].

Table 3. Top 10 countries applying pesticide at higher rates in 2000 [2].

Table 4. Top 10 pesticide companies in 2007 [3].

of food products [5,6]. The benefit/cost ratio vary from 4 to 33 (for every dollar spent on pesticide farmers receive an additional $4 - 33 in revenue) depending upon crop rotation and year [4,7].

After pesticides are applied to the target areas, pesticide residues remain in containers and application equipment. These residues are removed from applicators by rinsing with water which results in the formation of a toxic wastewater that can adversely affect people, pets, livestockand wildlife [8-10]. The resulting ecological impact of unsafe disposal of pesticides can be severe depending on the type of pesticide and the amount contained in the wastewater. The phenomenon of biomagnification of some pesticides has resulted in reproductive failure of some fish species [11,12] and egg shell thinning of birds such as peregrine falcons, sparrow hawk and eagle owls [13]. Pesticide toxicity to humans include skin and eye irritation and skin cancer [14]. Therefore, care must be exercised in the application, disposal and treatment of pesticides. Currently, disposal of pesticide wastewater is carried out by several methods including: 1) land cultivation, 2) dumping in soil pits, in ditches, in lagoons, on land, and in extreme cases in sewers and streams near the rinsing operation, 3) use of evaporation pond and 4) land filling. These methods of disposal are totally unsafe. The surface run off will reach streams, rivers and lakes and the infiltration of the wastewater into the local soil will eventually end up in the ground water. The treatment methods currently used for pesticide containing wastewater include: 1) incineration, 2) chemical treatment, 3) physical treatment and 4) biological treatment. These treatment methods either require land or are expensive and suffer from variability of effectiveness [15]. Thus, the development and selection of safe, on farm disposal/treatment technique for agricultural pesticides is paramount.

The aim of this study was to review the current methods of disposal and treatment of pesticides and to perform a comparative analysis to determine the most appropriate method for on farm use.

2. Pesticide Disposal Methods

The methods for the disposal of low level pesticides (Table 5) include: land cultivation, disposal pits, evaporation ponds and landfills [16-20]. There are three types of disposal pits: soil pit, plastic pit and concrete pit.

2.1. Land Cultivation

In this method, excavated contaminated soil is spread out in a thin layer on uncontaminated soil (Figure 1) in order to allow for natural chemical and biological processes to transform and degrade the contaminants. Soil contains microbes (fungi, algae and bacteria) capable of

Table 5. Disposal methods of pesticide containing wastewater.

Figure 1. Land cultivation of contaminated soil [21].

metabolizing pesticides [22,23]. The ability of bacteria to metabolize pesticides has been well documented by several researchers. Bhadhade et al. [24] reported that soil bacteria was capable of degrading 83% - 93% of the organo-phosphorouspesticide monocrotophos. Ohshiro et al. [25] reported a 96% reduction in isoxathion from the organophosphouruspestiside by bacteria isolated from turf green soil. Kearney et al. [26] reported that soil microbes were capable of degrading 90% of the alachlor pesticide within 30 - 40 days. Tang and You [27] reported that the triazophos bacteria was capable of degrading 33.1% - 95.8% of pesticides in soil.

Racke and Coats [28] reported that after soil has been treated with a pesticide a few times its microorganisms build up a need for that pesticide which results in fairly rapid degradation of any additional applications. Schoen and Winterlin [29] stated that natural soil degradation is effective when low concentrations of the pesticide are present, but with high concentrations of pesticide it becomes much more difficult to degrade. Felsot [30] stated that land cultivation is only effective for compounds that can be biotransofrmed or biominerlized by soil microbes. Somasundaram et al. [31] reported that the ability of soil microbes to degrade certain pesticides is affected by pesticide toxicity to soil microbes that are responsible for the degradation. Felsot et al. [22] stated that land cultivation is effective if the pesticide is degraded at the same or faster rate than it is applied to the field. Felsot et al. [32] noted that land cultivation can be enhanced by the addition of organic amendments such as sewage sludge.

2.2. Soil Pit

A primary method for disposing of liquid pesticide waste is by dumping it in an unlined soil evaporation pit (Figure 2), usually 15 × 15 × 1 m [33]. Schoen and Winterlin [29] reported that factors such as chemical structure and concentration of pesticide play a major role in the degradation of pesticides in soil pits. Gan and Koskinen [34] stated that the dissipation of the pesticide decreases as the concentrations of pesticide increases. Dzantor and Felsot [35] and Gan et al. [36] noted that high pesticide concentrations may cause microbial toxicity which would inhibit the degradation of the pesticide.

Several researchers [22,34,36,37] noted that the prolonged dissipation of pesticides opens a window for runoff and leaching, especially at higher pesticide concentrations. Gan et al. [36] reported that 50% dissipation of the alachlor pesticide in soil, at concentrations of 4 and 4 300 mg/kg took approximately 2 and 52 weeks, respectively. Gan et al. [38] noted that atrazine pesticide took approximately 4 and 24 weeks to be dissipated to half the concentration of 7 and 6400 mg/kg in soil, respectively. Schoen and Winterlin [29] noted that captan, trifluralin and diazinon at concentrations of 100 mg/kg took 1 - 2, 116 - 189 and 77 - 160 weeks to dissipate to half the concentration while captan, trifluralin and diazinon at concentrations of 1000 mg/kg took 30 - 48, 168 - 544 and 77 - 160 weeks to reach 50% disappearance in soil, respectively.

2.3. Plastic Lined Pit

This method for disposal of pesticide waste requires proper selection of the site to avoid leaching and runoff.

Figure 2. A soil pit for disposal of pesticide water [33].

The site should be in an area where there is no danger of contaminating dwellings groundwater sources and surface water used for crop and livestock production. The pit should be on a levelled ground with a depth of 0.5 - 1 m covered with a plastic liner and a layer of soil is laid on top of the liner (Figure 3). The pit should be open to the atmosphere in order to allow for water evaporation into the atmosphere. A roof cover will prevent the water level from raising due to rain or snow. The wastewater is pumped into the pit for pesticide biodegradation by soil microbes [22]. Hall et al. [20] reported that the presence of microbes in the soil water mixture in plastic lined pits was responsible for the degradation of pesticide and no accumulation of pesticide was noted in the pits. Junk and Richard [39] evaluated the effectiveness of 90,000 L polyethylene lined disposal pit with over 150 kg of 25 different types of pesticides for over 2 years and concluded that this method was in fact effective for disposal of pesticide waste with insignificant release to air and water surroundings.

Figure 4 illustrates a cross section view of a simple small scale plastic pit used to dispose of pesticide waste. It consists of a plastic drum with a length and width of 75 × 55 cm, respectively. Inside the drum is a mixture of 15 kg of soil and 60 L of water, that was used to treat pesticide waste which was introduced into the system through the inlet. Junk et al. [19] used 56 plastic containers filled with 15 kg of soil and 60 L of water to test the degradation of alachlor, atrazine, triflualin, 2,4-D ester, carbaryl and parathion and found this system not suitable for atrazine but was effective and very rapid for 2,4-D and carbayl. They concluded that: 1) the plastic container

Conflicts of Interest

The authors declare no conflicts of interest.

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