THE EFFECT OF NATURAL DYE EFFLUENT ON THE ENVIRONMENT ABSTRACT

Transcription

1 THE EFFECT OF NATURAL DYE EFFLUENT ON THE ENVIRONMENT P.M. Chan, C.W.M. Yuen and K.W.Yeung Institute of Textiles and Clothing, The Hong Kong Polytechnic University ABSTRACT The performance of waste-extracted natural dyes and mordants with respect to the environment has been verified and suggested to be comparable to the traditional mordants containing heavy metals. It is interesting to perceive that the COD/BOD 5 ratio of these natural dyes is approximately 2, which is an aspired ratio for effluent treatment. Moreover, the absence of restricted heavy metals in natural mordants enhances their application in dyeing process. In a nutshell, the potential for developing natural dyes and mordants are unlimited. 1. INTRODUCTION In response to the green movement and ecological campaigns, some dye manufacturers might be re-considering the feasibility of adopting natural dye in lieu of synthetic dye in dyeing process. Since the adoption of natural dyes may lead to the problems of poor dye uptake and low colour fastness, it is quite logical for them to introduce a traditional mordant to resolve the situation. In common practice, the traditional mordants adopted fall mainly within the group of heavy metal category. The heavy metals detached from these traditional mordants, however, will contaminate the water and poison the environment, thereby jeopardising the original intention of using environmentally friendly dye for better protection of the environment. In this paper, attempts have been made to extract natural dyes from the common waste products such as tea residues and wilted flower petal, and also natural mordants from eggshell and curcumin, which were subsequently applied into the wool dyeing process [1-7]. The contents of dye effluent including Biochemical Oxygen Demand (BOD 5), Chemical Oxygen Demand (COD), turbidity, heavy metal and ph parameters were investigated. The effect of dye effluent on the environment was evaluated by comparing the content of original dye bath containing no mordant (NM) with that of other dye baths containing waste-extracted natural mordants (M) or traditional mordants, i.e. alum (Al), copper sulphate (Cu), ferrous sulphate (Fe), potassium dichromate (Cr) and tannic acid (Ti). Optimum COD/BOD 5 ratio has proved that the treatability of the natural dye effluent is more manageable than the corresponding synthetic dye effluent. 2. EXPERIMENTAL 2.1 Extraction of Simulated Tea Dyes A minute scale of simulating Chinese tea residues was carried out by soaking the tea leaf in boiling water for 5 minutes. The tea solution was discarded and the soaked tea leaf was then dried and kept as a source of tea dye. The dye solution was prepared by boiling 10g of tea dye in 1000ml of de-ionised water at 100 o C for 1 hour. The filtered tea dye solution was used for the subsequent experiments. 57

2 2.2 Extraction of Flower Petal Dyes 30g of flower petals were boiled in 1000ml of de-ionised water for 1 hour. The filtered dye solution was used for the subsequent experiments. 2.3 Application of Mordanting Two natural mordants namely eggshell and curcumin were selected for tea dyes and flower petal dyes respectively g eggshell was extracted using 100 ml of 54.09% acetic acid at o C. The resultant eggshell solution was diluted for 10 times. The curcumin with 98% purity was purchased from a chemical supplier, Aldrich. 0.35g curcumin was dissolved in 100 ml of 98% ethanol to make curcumin solution. Five traditional mordants namely alum, copper sulphate, ferrous sulphate, potassium dichromate and tannic acid were also selected for both tea dyes and flower petal dyes. 10g of wool fabrics were padded with natural mordant solutions or 10g/l traditional mordant solutions followed by drying and then curing at 70 o C for 2 minutes. 2.4 Dyeing of Pre-Mordanted Wool Fabric with Tea Dye and Petal Dye Solution AHIBA NUANCE Top Speed produced by Datacolor International Limited was used to dye 2g of pre-mordanted wool fabric with 10g/l tea dye solution or 30g/l flower petal dyes of liquor ratio 50:1 at ph 4 and 70 o C for 90 minutes. 2.5 Testing on Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Turbidity, Heavy Metal and ph of Natural Dye Effluent 2, 5 and 10ml of the original dye effluent were placed separately in BOD bottles followed by making up to the mark with dilution water. The testing procedures were based on the ISO 5815:1989 (E). The testing methods of COD and turbidity were based on the ISO 6060:1989 (E) and ISO 7027:1990 (E) respectively. To detect a traceable amount of heavy metals present in the dye effluent, the technique of inductively coupled plasma (ICP) was used. The ph value of dye effluent was measured by ph meter. 3. RESULT AND DISCUSSION Biochemical Oxygen Demand (BOD) BOD is defined as the oxygen required for oxidising the biodegradable organic matters in the water or waste water samples through biochemical process. It is, in fact, a measurement of the organic strength of the samples. Table 1 shows the BOD 5 results of tea dye and flower petal dye effluents respectively after wool dyeing. 58

3 Table 1: BOD 5 (mg/l) of natural dye effluents containing various types of mordant Lung Ching Tikuanyin Oolong Black Flower Rose petal dye Carnation The results showed that the BOD 5 values of tea dye effluent were ranging from mg/l to mg/l. The trend of increment depended on the degree of fermentation of tea dyes, e.g. the non-fermented tea dye such as Lung Ching tea showed lower BOD 5 while the heavily fermented tea dye such as Black tea showed higher BOD 5. The BOD 5 values of Tikuanyin and Oolong tea were in the middle range. Within the same type of tea dye, different kinds of mordants showed very little influence on the resultant BOD 5 values. This implied that the heavy metals present in the dye bath would not affect the performance of bacteria during the degradation of the organic matters in the biochemical process. On the other hand, the BOD 5 values of rose petal dye and carnation petal dye were within the range of mg/l to mg/l. The overall variation of BOD 5 between different mordants used in dyeing process was relatively less. Since the total amount of organic matters present in these two flower petal dyes was similar, thus the major contribution of BOD 5 content was probably due to the flower petal dye but not the mordant. Chemical oxygen demand (COD) COD is defined as the mass concentration of oxygen equivalent to the amount of dichromate consumed by dissolved and suspended matter when a water sample is treated with the oxidant under the defined condition. Table 2 shows the COD results of tea dye and flower petal dye effluents respectively after wool dyeing. Table 2: COD (mg/l) of natural dye effluents containing various types of mordant Lung Ching Tikuanyin Oolong Black Flower Rose petal dye Carnation With regard to the definition of COD and BOD 5, the former is used to reflect the mass concentration of oxygen equivalent to oxidise the dissolved and suspended matter of both organic and inorganic matter, while the latter is used to determine the oxygen required for oxidising the biodegradable organic matter only. Hence, the result of COD has a high correlation with the results of BOD 5. In other words, the result of BOD 5 can be envisaged as a partial answer to anticipate the COD value. The COD values of natural dye effluent are always larger than the BOD 5 values but their increment trend is similar. 59

4 The results obtained illustrated that the COD of tea dye effluent varied within the range of mg/l to mg/l, and the COD of flower petal dye effluent varied within the range of mg/l to mg/l. In the dyeing industry, the results of BOD 5 and COD are seldom compared individually. The treatability of effluent is judged by measuring the ratio of COD to BOD 5. If the ratio is high, the treatability of the effluent will be very difficult implying that the biodegradability is low. The treatability of effluent depends mainly on the volume and strength of effluent. Table 3 shows the results of COD/BOD 5 ratio of tea dye and flower petal dye effluents. Most of the biological waste treatment plants prefer the COD/BOD 5 ratio equal to 2. For textile operations, the COD/BOD 5 ratio is ranging from 1.6 to 6.0 and the average of dye house effluent is approximately 3.0. In the experimental result, the COD/BOD 5 ratio of natural dyes was ranging from to with an average value around 2. This confirmed that the treatability of natural dye effluent was higher when compared with the dye house effluent, meaning that the natural dye effluent was highly biodegradable which was anticipated by most waste water treatment plants. Table 3: COD/BOD ratio of natural dye effluents containing various types of mordant Lung Ching Tikuanyin Oolong Black Flower Rose petal dye Carnation Turbidity Turbidity is a measurement of the passage of light through water. Suspended matters and colloidal particles present in water are the major compounds that cause the turbidity. Higher turbidity generally corresponds with a lot of suspended particles present inside the effluent that will require more times to be digested. It also relates to poorer environmental condition. Table 4 shows the turbidity of both tea dye and flower petal dye effluents. The overall results showed that the turbidity caused by natural mordants was ranging from 40 to 170 NTU which was relatively low and acceptable when compared with that of the traditional mordants. Table 4: Turbidity (NTU) of natural dye effluents containing various types of mordant Lung Ching Tikuanyin Oolong Black Flower Rose petal dye Carnation Heavy metal content In order to minimise any further nuisance to the environment, United State has been imposing strict environmental legislation hoping to limit the heavy metal contents such as Cr, Ni, Cu, 60

5 Cd, An, Pb and Sn etc. under 2ppm in the effluent discharged from dye house. Though the requirements are not as strict as in USA, the Hong Kong Government has already imposed standards on effluents discharged into foul sewers before reaching the Hong Kong Government sewage treatment plants. Strict regulations have been established to limit the amount of heavy metal present in the dye effluent in different countries. Emphasis is currently being placed on the reduction of trace metals in textile processing effluent. Certain amounts of metals detached from the pre-mordanted wool fabric during dyeing are illustrated in Table 5. There was no sign of aluminium, copper, iron, and chromium present in the original dye bath containing no mordant. When compared, the aluminium present in the alum mordant detached very seriously during dyeing process. Fortunately, aluminium was not included in the restricted list and so it would not cause any adverse effect on the effluent discharge. On the contrary, the amount of copper, iron and chromium present in the dye effluent was found to exceed the ceiling of acceptable limit required by both USA and Hong Kong standards. Table 5: Heavy metal content (ppm) of natural dye effluents containing various types of mordant Flower petal dye NM Al Cu Fe Cr Lung Ching Tikuanyin Oolong Black Rose Carnation ph ph is a measurement of the hydrogen ion concentration in water. Low ph refers to acidic condition while high ph refers to alkaline condition. The ph of water affects many chemical and biochemical reactions involved in both water and waste water treatment. It is one of the most commonly measured parameter in public health engineering. Since the dyeing of wool fabric with natural dyes was carried out in acidic medium, i.e. ph 4, thus the ph of dye effluent generally would not exceed the legal limit of Table 6 illustrates the ph values of both tea dye and flower petal dye effluents. Table 6: ph of natural dye effluents containing various types of mordant Flower petal dye Lung Ching Tikuanyin Oolong Black Rose Carnation CONCLUSION The results of BOD 5 illustrate that the traditional mordants containing heavy metal will not affect the performance of bacteria during the degradation of the organic matters in the biochemical process. The organic matters originated from natural dyes are the dominant factor to determine the BOD 5 values. From environmental point of view, the COD/BOD 5 61

6 ratio of most of the dyeing processes using natural dyes in conjunction with natural mordants is near 2, implying that the natural dye effluent is highly environmentally biodegradable and treatable. Although eggshell contains a lot of calcium, its presence in the dye effluent does not impose adverse effect on the environment. On the contrary, the amount of copper, iron and chromium detached from the pre-mordanted fabric does exceed the ceiling of acceptable limit required by both USA and Hong Kong standards. In conclusion, the use of wasteextracted natural mordant to replace harmful traditional mordants is feasible and can offer a partial answer to ecological environment that demands attention and exploration. ACKNOWLEDGEMENT One of the authors (P.M. Chan) wishes to acknowledge a studentship received from The Hong Kong Polytechnic University Postgraduate Block Grant for the work reported here. REFERENCES Agarwal A., Paul S. and Gupta K. C., 1993, Effect of Mordants on Natural Dyes, The Indian Textile Journal, January, pp Chan P.M., Yuen C.W.M. and Yeung K.W., 1997, A Study of Dyeing Properties of Colourants Extracted from the Natural Waste Green Products, Proceeding of the 4 th Asian Textile Conference, Taipei, R.O.C., Vol. II, June, pp Chan P.M., Yuen C.W.M. and Yeung K.W., 1998, An Utilization of Waste Materials in Dyeing Process, Proceeding of the 3 rd International TEXSCI Conference, Czech Republic, Vol. 3, May, pp Chan P.M., Yuen C.W.M. and Yeung K.W., 1997, Dye from Tea, Textile Asia, Vol. XXVIII, No. 10, October, pp Chan P.M., Yuen C.W.M. and Yeung K.W., 1997, Dyeing Behavior of Green Dyes in Coloration Process, American Chemical Society 213 th National Meeting, Book of Abstracts, Part 1 : CELL112, April, Chan P.M., Yuen C.W.M. and Yeung K.W., 1998, Natural Dyes and Their Application, Textile Asia, Vol. XXIX, No. 5, May, pp Dyer A., 1976, Dyes from Natural Sources, Charles T. Branford Company, Newton, Mass., pp