191 an OVERVIEW of the PHENOL LEVELS in WASTEWATER in the CITY of CAPE TOWN SMITH a City of Cape Town, Scientific Services Branc
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191 AN OVERVIEW OF THE PHENOL LEVELS IN WASTEWATER IN THE CITY OF CAPE TOWN SMITH A City of Cape Town, Scientific Services Branch, P.O. Box 16548, Vlaeberg, 8018, Tel: (021) 684 1049, Fax (021) 6385083, e - mail: [email protected] ABSTRACT Widespread contamination of water by phenol has been recognized as an issue of growing importance. Phenol may occur in domestic and industrial wastewaters, natural waters and potable water supplies. Chlorination of such waters may produce odorous and objectionable tasting chlorophenols. Therefore, it is necessary to eliminate as much of the phenol from the stream before discharging. The limit for phenol in the wastewater final effluent according to the General Standards Guideline is 0.1mg/l and in 2010 it will be 0.01mg/l (5). Hence, the treatment of wastewater containing phenol is a necessity. This study gives an overview of the Phenol index levels (free phenol) in wastewater in the City of Cape Town. There is no real historic data to compare the current phenol levels in the wastewater with but it can be assumed that levels will increase over time if more stringent measurements are not taken to prevent the discharge of higher levels of phenol into the rivers. There are twenty wastewater treatment plants and three marine outfalls in the City of Cape Town. The wastewater treatment plants can be classified as receiving mainly industrial or domestic wastewater or a combination of the two. The raw influent and final effluent results for each wastewater treatment plant were sampled bi- weekly and analysed for free phenol. The influent and effluent wastewater was analysed in order to establish if there is a change in phenol concentration during the treatment process. The average influent levels ranged from 0.06 mg/l up to 0.529 mg/l. The highest was found in the Klipheuwel treatment plant. The average effluent level ranged from 0 mg/l up to 0.061 mg/l with the highest recorded also in the Klipheuwel treatment plant. Removal of phenol occurred in the range of 69 % up to 100 %. INTRODUCTION Phenol is one of the most common organics contained in waste streams that originates from the chemical process industries but it is also a natural substance. It is used as a disinfectant and is found in a number of consumer products, including mouthwashes, gargles and throat lozenges. Low levels of phenol can also be present in air and in drinking water. It is not known if phenol causes cancer in humans but cancer developed in mice when phenol was applied to the skin several times per week for the lifetime of the animal. Phenol did not cause cancer in mice or rats that drank water containing it, for 2 years (1). Apart from being a suspected carcinogen, Phenol and some of its derivatives can also be toxic or lethal to aquatic life. When Phenol enters the environment it has a half-life in soil between 1 and 10 days. It has a half-life in water between 10 and 30 days. Larger or repeated releases of phenol can remain in the air, water and soil for much longer periods. Phenol does not build up in fish, other animals, or plants but is expected to be toxic to aquatic life with a LC50/96-hour value for fish between 10 and 100 mg/l. Low phenol levels in the parts per billion range gives water a disagreeable taste and odour (2). Phenol may occur in domestic and industrial wastewaters, natural waters and potable water supplies. Chlorination of such waters may produce odorous and objectionable tasting chloro-phenols. Therefore, it is necessary to eliminate as much of the phenol from the stream before discharging. The limit for phenol in the wastewater final effluent according to the General Standards Guideline is 0.1mg/l and in 2010 it will be 0.01mg/l. (5) SURVEY There are twenty wastewater treatment plants and three marine outfalls in the City of Cape Town. The treatment plants can be classified as receiving mainly industrial or domestic wastewater or a combination of the two. Table 1 gives a summary of the classifications. TABLE 1: Classification of the wastewater treatment plants MIXED DOMESTIC MAJORITY DOMESTIC INDUSTRIAL Cape Flats Landudno Klipheuwel Wesfleur industrial Potsdam Wesfleur domestic Gordens Bay Athlone Mitchells Plain Borcherds Quarry Simons Town Kraaifontein Millers Point Bellville Wildevoelvlei Melkbosstrand Parow Maccassar Zandvliet Scottsdene All these plants have biological treatments, either activated sludge or trickling filters (3). The raw influent and final effluent for each plant was analysed every second week. The aim was to establish if there is a change in phenol concentration during the treatment process. The free phenol concentration was determined using the Aquakem Discreet Analyser. CHEMICALS 4-Aminoantipyrine reagent Potassium Ferricyanide Solution Buffer Solution 1mg/l Stock Phenol solution INSTRUMENTATION Method Summary: Phenolic materials react with 4-aminoantipyrine in the presence of potassium ferricyanide at a pH of 10 to form a stable reddish-brown colored antipyrine dye. The amount of color produced is a function of the concentration of phenolic material. The absorbance of the color produced is measured at 510nm. METHOD Sampling: Most of the raw samples were composited over a twenty four-hour or eight-hour period but for the smaller plants grab samples were taken. Grab of composite final effluent samples for each plant were taken at more or less the same time as the raw. Sample preparation: Samples were filtered into the sample tubes using a syringe and 0.45 μm syringe filters. RESULTS Table 2 gives a summary of the influent and effluent results obtained for each wastewater treatment plant. Included in the table is the type of treatment at each plant. Table 2: Summary of the results obtained PLANT CHEM. RANGE AVE. CONC. AVE TREATMENT mg/l mg/l % TYPE REMOVAL Cape Flats INFL 0.016 – 0.377 0.221 92 Activated sludge EFFL 0 – 0.106 0.018 Potsdam INFL 0.05 – 0.420 0.335 100 Biofilter EFFL 0 0 Activated sludge Athlone INFL 0.036 – 0.487 0.260 81 Activated sludge EFFL 0.032 – 0.058 0.050 Borcherds INFL 0.097 – 0.498 0.259 100 Activated sludge Quarry EFFL 0 0 Kraaifontein INFL 0 – 0327 0.201 100 Biofilter EFFL 0 0 Activated sludge Bellville Orb INFL 0.04 – 0.262 0.203 100 Activated sludge EFFL 0 0 (Orbal) Bellville DA INFL 0.04 – 0.347 0.159 94 Activated sludge EFFL 0 – 0.019 0.010 Landudno INFL 0 – 0.205 0.060 100 Biocontractor EFFL 0 0 Wesfleur INFL 0.077 – 0.333 0.247 100 Activated sludge Domestic EFFL 0 0 Klipheuwel INFL 0.082 – 0.987 0.529 88 Biocontractor EFFL 0 – 0.181 0.061 Gordons Bay INFL 0.059 – 0.403 0.201 100 Activated sludge EFFL 0 0 Mitchells Plain INFL 0.030 – 0.364 0.181 100 Activated sludge EFFL 0 0 Simons Town INFL 0 – 0.117 0.058 69 Biofilter EFFL 0 – 0.111 0.018 Millers Point INFL 0 – 0.250 0.084 100 Biocontractor EFFL A 0 0 EFFL B 0 0 Wildevoelvlei INFL 0.037 – 0.272 0.134 100 Activated sludge EFFL 0 0 Melkbosstrand INFL 0.005 – 0259 0.145 100 Activated sludge EFFL 0 0 Parow INFL 0.084 – 0.499 0.259 97 Activated sludge EFFL 0 – 0.037 0.009 (Orbal) Maccassar INFL 0.025 – 0.112 0.060 82 Activated sludge EFFL 0 – 0.064 0.011 Zandvliet INFL 0.049 – 0.413 0.180 93 Activated sludge EFFL 0 – 0.024 0.013 Scottsdene INFL 0.090 – 0.483 0.318 99 Activated sludge EFFL 0 – 0.009 0.002 Wesfleur INFL 0.005 – 0.383 0.266 80 Activated sludge Industrial EFFL 0.029 – 0.071 0.052 DISCUSSION From the results in Table 2, It can be seen that the highest average influent phenol level of 0.529 mg/l was recorded for Klipheuwel treatment plant which is a plant receiving a majority of domestic waste while for a plant receiving a mixture of domestic and industrial waste, the highest was recorded for Potsdam with a average of 0.335 mg/l. The only plant receiving purely industrial waste is Wesfleur Industrial plant where an average of only 0.266 mg/l was measured. The lowest average influent level of 0.058 mg/l was measured for Simons Town treatment plant, which is also a plant receiving majority domestic waste. Over weekends, at present, leachate from a hazardous landfill site is dumped at the Cape Flats treatment plant, of which the phenol level can range between 20 and 30 mg/l. Because the weekly Cape Flats samples are only sampled on a Monday, the influent concentration does not reflect this. The percentage removal rate of the different treatment plants ranges from an average of 69% for Simons Town treatment plant to an average of 100% for 11 of the 20 treatment plants. Most of the removal rates are above 90%. It has been documented that one way of treating Phenol in wastewater is through biological treatment. As mentioned before, all the treatment plants have biological treatments, either activated sludge or trickling filters and the question therefore is whether the applicable treatment process is sufficient. FURTHER STUDIES Further studies are planned in which the influent and effluent samples of two plants will be taken over a 24 or 48 hour period (depending on the flow/treatment rate of the particular plant) in order to see if the phenol levels going in to the plant are carried through to the effluent and if the biological treatments is sufficient to treat the phenol in the wastewater.