BUFFALO RIVER, EASTERN CAPE
4.3 S TUDY SITE
4.6.2 Textile effluents
The chemical source of textile effluent toxicity has been discussed at length in Section 4.1.2. The effluent was coloured as dyes and surfactants are passed onto the effluent during the manufacturing process. The combination of strong colour and high TDS levels lead to effluent turbidity in the experimental channels and it was difficult to see test organisms at high effluent concentrations. This could have also interfered with organism feeding. The GTE was more turbid than PITE; suggesting that turbidity
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could have contributed to the death of organisms by clogging the gills. Effluents from the dyeing process are also toxic, and as most dyes are not biodegradable, they are not effectively removed during biological treatment.
Wool scouring is the major source of pollution in the textile industry (Correia et al., 1994), and therefore could have rendered the GTE toxic, as some scouring effluent is passed on to the next step of the manufacturing process. This textile mill uses hypochlorite for bleaching, and residuals and by-products would affect aquatic organisms ( Nicolaou and Hadjivassilis, 1992).
In this study, the GTEs were generally found to be acutely toxic, which could be attributed to the fact that there is no secondary treatment, or any form of biological treatment before the effluent is released and used for irrigation. Treated textile effluent has been found not to be toxic (Altinbas et al., 1995; Davies and Cottingham, 1994; Nicolaou and Hadjivassilis, 1992). The PITE was not acutely toxic although this effluent does not go through any form of biological treatment. There is a possibility that some substances become trapped in the soil or grass roots during irrigation, as the PITE is a run-off effluent from irrigation. Ions such as Ca2+ cations and Cl- anions, are washed down into the holding dam, showing up as high levels of calcium and chloride in the PITE (Table 4.13). It has also been shown that Ca2+ has an ameliorative effect on toxicity (Palmer and Scherman, in press). There is also a possibility that non-toxicity is due to the fact that the effluent goes through a stabilization period in the holding dam (Tailwater Dam), where some substances such as trace metals attach onto suspended solids and settle at the bottom. Substances such as organics may also be degraded in the Tailwater Dam, rendering the effluent less toxic.
Effluent salinity
Information on the effects of salinity on riverine indigenous invertebrates (site- specific testing) appears to be scarce. The Centre for Aquatic Toxicology, at the Institute for Water Research, Grahamstown, initiated toxicity testing using indigenous riverine mayfly larvae, and selected salinity as the first water quality variable under
investigation. In the present study, textile effluent was used as a complex, saline whole effluent. Results showed that toxicity was not due only to increasing EC levels, as GTE and PITE exhibited similar Na+, SO42-
and TDS levels, which contribute to salinity, and yet PITE was not acutely toxic. Calcium levels were however higher in the PITE (17 – 19 mg/l) than in the GTE (2 – 6 mg/l). The ameliorative effect of Ca2+
on salinity toxicity (Palmer and Scherman, in press), may have contributed to the reduced toxicity of the PITE. It is possible that the effluent salinity was not so high as to lethally affect organisms.
Generally, the salinity of the Buffalo River in the upper reaches is low (DWAF, unpubl. data), but discharges of treated and untreated sewage effluents and industrial effluents, such as tannery and textile effluents, have altered its salinity in the middle reaches. Salinity gradually increases as the river passes the industrial area, and decreases again to less than 50 mS/m, as the water leaves the Laing Dam. This indicates that self-cleansing takes place, and the dam acts as a settling reservoir. At Mc Tyre Bridge, a DWAF sampling point below the discharge point of the Mlakalaka stream, the salinity was higher by 2 folds than above the discharge point (DWAF, unpubl. data). The discharged textile effluent contributes to this increase in salinity.
Salinity of textile effluents used in this study was 15 to 20 times that of the unimpacted Buffalo River water (at the sampling site), and has to some extent contributed to the increased salinity of the river. This becomes more evident during low flows, as the salinity of the Buffalo River middle reaches increase sharply (DWAF, unpubl. data). According to the present license conditions, the textile mill is allowed to discharge effluent with EC not greater than 250 mS/m. The new National Water Act (No 36 of 1998) has decreased the allowable EC to the maximum of 200 mS/m for irrigation (DWAF, 1999b).
Colour
Historically, textile effluents have a major environmental impact on rivers in industrial areas. As a result, the National Rivers Authority in the United Kingdom has set standards to protect key rivers affected by textile effluents, and has set target dates for compliance with the standards (ENDS Report, 1993). This has put pressure
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on textile industries and Sewage Treatment Works. The Sewage Treatment Works were forced to reduce the levels of colour permitted in their trade effluent standards in order to comply. Colour is one of the most pressing problems facing the textile industry, and has the highest public profile. Up to 50% of the initial dye load will be found in the effluent (ENDS Report, 1993), giving rise to highly coloured effluent, which is difficult to treat.
The textile mill in this study is discharging coloured effluent into the receiving water via the Mlakalaka stream, as there are no strict regulations prohibiting the discharge.
The strong colour of the textile effluent caused some change in the river water below the point of discharge. The colour change can cause a considerable disturbance to the ecological system of the receiving water.