Table 1.

Advantages and disadvantages of different dye wastewater treatment methods.

Method	Rationale of method	Advantages	Disadvantages	Reference
Biological Methods	Uses different microbes like bacteria fungi, algae, yeast and enzymes to degrade and decolourise dyes	-Simple, economically attractive and environmentally friendly process -Large number of species can be used in consortiums or pure cultures e.g. bacteria, fungi -Good dye removal efficiency -High removal of biochemical oxygen demand and suspended solids (BAS) -Anaerobic bacteria are suitable for large scale application	-Requires optimally favourable environment -Requires management and maintenance of the microorganisms and/or physicochemical pre-treatment -Slow process -Generation of biological sludge and uncontrolled degradation products	[10, 11, 12]
Adsorption	Uses different types of adsorbents like plant biomass and activated carbon to remove pollutants through the process of adsorption	-Good dye removal efficiency -Short reaction time	-Challenge in regeneration of adsorbents, -Generates toxic by-products: no mineralisation of dyes -Not applicable to all dyes -Requires precise control of process conditions e.g pH	[11, 13, 14]
Coagulation	Uses coagulants such as alum to form flocs that settle colloidal particles together with dye molecules	-Technologically simple process -Highly effective in eliminating metals -Good dye removal efficiency	-Large chemical consumption -Produces sludge -Requires precise control of process conditions e.g. pH	[11, 15, 16]
Advanced oxidation	Uses free radicals mainly hydroxyl radicals generated from ozone, UV radiation and hydrogen peroxide to degrade dye molecules	-High dye removal efficiency -possibility of dye mineralisation -Short reaction time -Low chemical consumption -No production of sludge -Dye mineralisation	-Cost intensive -Produces undesirable by-products -Requires precise control of pH	[11, 17]
Membrane filtration	Uses pressure to remove pollutants by passing them through a membrane with a defined pore size either through macrofiltration, microfiltration, nanofiltration or reverse osmosis	-Simple process -Highly efficient -Environmentally friendly: no chemicals are used -Easily applicable in actual industrial applications	-Membrane fouling -High energy and maintenance costs -High initial setup costs -Poor dye mineralisation	[11, 18]
Electrochemical treatment	Uses oxidants generated in-situ via redox reactions on the surface electrodes to remove pollutants	-Highly effective in removing organic pollutants -Economic process -Easy to control process pH -Process does not use chemicals	-Cost intensive: High energy consumption -Generates secondary products	[11, 19, 20]