Wastewater is liquid discharged by domesticresidences, commercial properties, industry, agricultural processes whichcontain some contaminants that result from the mixing of wastewater fromdifferent sources (1). Industries particularly textile, food, paper and pulp manufacturingare known to consume large volumes of water during their daily operations. Theytherefore contribute a pro-rata amount of wastewater as effluent that ischaracteristic of their raw material properties. The use of synthetic chemicaldyes in various industrial processes, including paper and pulp manufacturing,plastics, dyeing of cloth, leather treatment and printing has increasedconsiderably over the last few years, resulting in the release ofdye-containing industrial effluents into the soil and aquatic ecosystems (2,3). This has led to the pollution of the environment with dyes which are noteasily degradable. In some cases, the dye solution can also undergo anaerobicdegradation to form potentially carcinogenic compounds that can end up in thefood chain (3). Moreover, highly colored wastewaters can block the penetrationof sunlight and oxygen, essential for the survival of various aquatic forms(3).
Dyesare colored substances that have an affinity tothe substrate to which they areapplied. They are generally applied inan aqueous solution, and may require a mordant toimprove the fastness of the dye on the fiber (4). Dyes are unique chemicalcompounds that react with a substrate in different ways depending on theirstructure.
While some react forming chemical bonds, others react physically andare as such easier to remove from their substrate. They can be classified basedon the source from which they are made, their chemical structure, nuclearstructure and on the basis of their industrial use. Other important classesbased on application have also been established. These include but are notlimited to leather dyes, fuel dyes, smoke dyes, solvent dyes, sublimation dyes. Dye wastewater can be defined as wastewater oreffluents discharged by industries, particularly the textile industry which arecontaminated with a dye or a mixture of dyes depending on the particularoperation. Color is the most prominent characteristic of dye wastewater even atlow concentrations and needs to be removed before wastewater can be discharged(5, 6). Theremoval of color from wastewaters is often more important than the removal ofthe soluble colorless organic substances, which usually contribute to the majorfraction of the biochemical oxygen demand (BOD).
Methods for the removal of BODfrom most effluents are fairly well established; dyes, however, are moredifficult to treat because their synthetic origin are mainly complex aromaticmolecular structures, often synthesized to resist fading on exposure to sweat,soap, water, light or oxidizing agents (2,3). In recent times, there have been stringentenvironmental laws regarding the treatment of effluents prior to discharge.This has necessitated the need for industries to embark on dye wastewatertreatment in order to adhere strictly to the set regulations. Consequently,various methods such as coagulation, adsorption, photo-catalytic decolorizationand oxidation, electrochemical method, ion exchange, membrane filtration anduse of ozone have been employed to treat dye wastewater. Biological treatmentprocesses are also used to treat dye wastewater.
These processes however aregenerally efficient for biochemical oxygen demand (BOD) and suspended solids removal(TSS) but are largely ineffective for removing color from wastewater (7, 8, 9).Generally, there are two decolorization methods; destruction of dyemolecules and separation of dyes from water (10, 11). Conventional methodsinvolved in the destruction or transformation of dyes such as such as chemical oxidation, photo-catalysis andbiodegradation (11, 12) have been found to be inadequate and require extensiveenergy to break down the dye molecules, most of which are stable to light,oxidizing agents and microbiological degradation (11,13,14,15). Separationmethods such as adsorption and membrane Adsorption of dyes on powder activatedcarbon is popular and effective (11). However, the activated carbon is notcheap, and the adsorption performance is reduced sharply after regeneration orreactivation, which also results in a 10–15% loss of the sorbent (16, 17, 18).Additionally, sorption methods are characterizedby low purification efficiency, especially, in terms of decolorization(19).
The use of ozone and hydrogen peroxide is very promising forenvironmental reasons but is very expensive when considering the quantityrequired to bring about the necessary wastewater treatment (19). Consequently,the need to surmount the demerits of individual processes has necessitated theuse of combined processes in order to enhance the overall treatmentperformance. Coagulation is widely used for dye removal due to its low capitalcost and simple operation (11, 18, 20, 21). Additionally, to achieve water withre-usable quality, an additional treatment stage requiring the use of amembrane at the ultimate step is required (22).
Pressure-driven membranes techniques such asultrafiltration (UF), microfiltration (MF), nanofiltration (NF) and reverseosmosis (RO) have been found to be effective in the removal of dyes fromwastewater. While reverse osmosis and nanofiltration have been used forefficient dye removal, the high energy requirement and operational costsassociated have made them less attractive. Ultrafiltration which has beensuccessfully used for separating high molecular weight and insoluble dyes fromwater (11), however, is not able to remove those water soluble dyes with lowmolecular weights (13, 23). Therefore, microfiltration is considered as arelatively cost-effective low-pressure membrane process especially as recentadvances in membrane technology have led to the reduction in cost of membranesand studies indicate that low-pressure membrane process appears to be a costeffective option (22, 24). Against this background, a coagulation-microfiltration hybrid technologyis used to treat and evaluate the extent of dye removal from textile wastewatersingly and a binary mixture of textile wastewater and fruit nectar wastewater. 1.2 OBJECTIVE The objective of this work is therefore summarizedbelow; Observing and studying the extent of color removal of different aqueoussolution of dyes against different coagulants singly and in the presence of acombined fruit drink wastewater of three different doses (low – 10ppm, medium –50ppm and high – 100ppm).
In lieu of theabove statement following objectives are to be considered: 1. Evaluation of the combined action ofcoagulation and microfiltration processes on the overall effluent qualityperceived through color removal and BOD removal.2. Studying the extent of color removal byincreasing coagulant doses through absorbance and transmissivity results.
3. Study the effect of coagulant dosage onthe removal of color, BOD and subsequent effluent quality of the combinedtextile effluent and fruit drink wastewater samples through absorbance andtransmissivity readings.4. Study the effect of dye strength on thecoagulation and microfiltration process.