Water reuse for the bottled water industry

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specific treatment to enable reuse of the effluent from the container washing machine. The analysis of water quality identified the following problems: high pH ...
E. Ramírez Camperos*, L. Cardoso Vigueros*, V. Escalante Estrada*, A. Gómez Navarrete*, A. Rivas Hernández* and E. Díaz Tapia** * Mexican Institute of Water Technology, Paseo Cuauhnahuac 8532, Col. Progreso, Jiutepec, Morelos, México, C.P. 62500 (E-mail: [email protected]) ** Coordinacion Industrial Mexicana S.A de C.V. Embotelladora de Toluca, S.A. de C.V.Paseo Adolfo Lopez Mateos 124, Zinacantepec, Edo de Mexico, México Abstract The bottled water industry uses a machine specifically designed for the washing of its containers (19-L capacity) and generates 6-L wastewater/container. This effluent can be used for watering of green areas and car washing. The objectives of the present work were to characterize the effluent and to propose a specific treatment to enable reuse of the effluent from the container washing machine. The analysis of water quality identified the following problems: high pH (10.0), high biochemical oxygen demand (50 mg/L), high concentration of free residual chlorine (3.15 mg/l), alkalinity (207 mg/l as CaCO3) and hardness (38.8 mg/l as CaCO3). These parameters must be reduced in order to comply with the Mexican standards for water reuse (NOM-003-ECOL-1997), and to protect the washing equipment against corrosion and incrustations. The water can be used for the watering of green areas after pH adjustment and Biological Oxygen Demand (BOD5) removal. If special equipment is used for car washing, it is necessary to reduce the concentration of calcium and magnesium using a strong cationic resin. Following these recommendations the specific industry installed a treatment system with pH adjustment, dual filtration (sand-anthracite) and adsorption system with activated carbon. The effluent is now used for watering of green areas and for car washing with garden hoses. Keywords Car washing; container washing; green area watering; purified water; water reuse

Introduction

The demand for purified water for daily consumption in Mexico increases every day, due to the fact that water cannot be drunk directly from the water distribution network. The production and sales of purified water is 5,600,000 m3 per year (INEGI, 1999). Water is sold in containers of different sizes; the 19-liter size is the most common for home consumption. The bottling industry uses 19-liter reusable plastic containers for the distribution and selling of purified water. The company itself picks up the reusable containers and returns them to be washed and refilled with purified water. A machine specifically designed for this purpose performs the container washing. The washing consists of four cycles: a pre-wash at room temperature; a wash with detergent at 80°C; a disinfecting wash, which consists of a wash with chlorine; and a final rinse. Once the washing is done, they are transferred to the filling area and subsequently to the final inspection area. The water that is consumed during the container washing is discharged without any further use. Even though this water contains detergents and chemical products used during the washing, it could be used for other purposes before its final discharge. The aim of this study is to measure and characterize the principal discharge obtained from the container washing machine and provide recommendations for its reuse in watering of green areas and car washing.

Water Science and Technology: Water Supply Vol 5 No 1 pp 101–107 © IWA Publishing 2005

Water reuse for the bottled water industry

Methods and materials

The analysis and characterization of the discharge were carried out in a bottling plant during a one-month period. Samples were taken from 8:00 to 23:00, which was considered enough time to obtain representative samples from the three washing shifts, and to cover

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the changes in the detergents and disinfectants used. The water obtained from the overall machine washing after its weekend maintenance was also characterized. The samples were taken directly at the exit of the water from the washing machine. Flow measurement was performed every hour. In order to characterize the container washing machine discharge water, simple and compound samples were taken for the following parameters: flow, pH, temperature, electrical conductivity, residual free chlorine, color, turbidity, greases and oils, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), detergents, settleable solids, total suspended solids (SST), total phosphorus, total nitrogen, faecal coliforms, total hardness, carbonate hardness, total alkalinity, phenolphthalein alkalinity and sulfate. In order to comply with the requirements of NOM-003-ECOL-1997, metals and cyanide were analyzed at the beginning and end of the study. Since cations were present in the abovementioned products, the cation analysis was also carried out. Results and discussion

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The washing machine discharge water had an average flow of 3.0 l/s with a standard deviation of 0.42 l/s, equivalent to a 14% variation. The discharge flow is constant during the washing period, variations are observed when the machine is stopped, either for a shift change, minor repair, or addition of a certain reagent, which generally diminishes the flow. The container washing effluent has an average pH of 10 units and a standard deviation of 0.369 units and a variation coefficient of 3.67%. This high pH value is due to the alkaline detergents used. The mean temperature of the container washing effluent was 31.2°C, with a standard deviation of 0.94 units and a variation coefficient of 3.05%. The temperature presents a variation after the tank cleaning. Turbidity was on the average 9.86 UTN with a standard deviation of 2.13 units and a variation coefficient of 21.7%. This parameter is due to the presence of suspended solids and other contaminants present in a suspended or colloidal form in the washing water. The color has an average of 46.27 Pt-Co units, with a standard deviation of 23.98 units and a variation coefficient of 51.82%. The color is mainly due to the light yellow color of the applied reagents and also as a result of the solids that might be removed from the containers during the washing. The free chlorine average was 3.15 mg/l, with a standard deviation of 0.54 units and a variation coefficient of 17.15%. Chlorine is a substance found in the disinfecting products used and also is added to the sanitation tank as sodium hypochlorite. The discharge variability is produced when a new chlorine compound is added or a spill occurs in the sodium hypochlorite tank. When this occurs, the concentration of residual free chlorine is from 4 to 6 mg/l. If chlorine is not added to the washing cycle, it will be depleted. Table 1 shows the average characteristics of the washing effluent. The average electrical conductivity in the container washing water was 806 µS/cm, which is equivalent to 403 mg/l of total dissolved solids, a standard deviation of 66.6 units and a variation coefficient of 26%. This conductivity is mainly due to sulfate, chloride, sodium, calcium, magnesium and potassium ions present in the sanitizing products. The average concentration of greases and oils was between 2 and 4.68 mg/l, however, extreme values as low as 0.1 mg/l and as high as 10 mg/l can be observed. These values could not be related to a specific event. The average biochemical oxygen demand (BOD5) was 50 mg/l with a standard deviation of 21.07 mg/l and a variation of 42%. Extreme values were obtained from 1.8 mg/l up to 96 ml/g. Daily average values of Biological Oxygen Demand (BOD5) vary from 22.7 mg/l to 91.5 mg/l, and surpass the maximum allowed limit that NOM-003-ECOL-1997 requires for water reuse in direct contact services. The COD fluctuated between 276 mg/l and 426.75 mg/l, this value is higher than the BOD5, which points out that the washing water contains low biodegradable compounds

Table 1 Average characteristics of the washing effluent Parameter

Range

3 l/s (259.2 m3/d) 10 31.2 9.86 46.3 3.15 806 3.2 50.1 346 15