Most of the dyes are organic compounds, with different degree of polarization and different groups with various steric effects, making their complete biodegradation slow or even impossible. Adsorption on fly ash and fly ash based substrates represents a possible alternative for simultaneous removal of dyes and heavy metals form wastewaters resulted in the textile industry. Adsorption (under visible light) and adsorption and photodegradation (under UV irradiation) studies were done on Methylene blue solutions and on their mixtures with heavy metals (copper and cadmium), in systems using fly ash as single substrate, or mixed with a wide band gap semiconductor (TiO 2 ). The titanium oxides and hematite content in fly ash proved to be responsible for photodegradation processes even in the absence of the TiO 2 powder, confirming that modified fly ash is a viable candidate in developing up scalable processes for advanced wastewater treatment. The kinetic and thermodynamic studies allow to calculate the parameters and to describe the complex mechanisms, involving competitive adsorption.

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The studies of Cu (II) adsorption were conducted by testing various sawdust types. Two biomass, oak sawdust wood (Querqus robur) and white poplar sawdust wood (Populus alba), have been compared considering their efficiency for copper removal from diluted water solutions. Raw sawdust proved no efficiency in adsorption. Therefore, pre-treatment processes were developed and optimized, to enhance the sawdust affinity for heavy metals adsorption. The optimized pre-treatment conditions are: solventaqueous solution of NaOH 3n at 22°C and a contact time 60 min for oak sawdust, respectively 30 min for poplar sawdust. The treated samples allow Cu(II) ions removal efficiency of 89% on oak sawdust and 67% on poplar sawdust. Metal ion sorption increased as the ratio of metal solution to the biomass quantity decreased. The increase of the metal ion concentration resulted in a steep increases in biosorption at lower concentrations, progressively reaching a plateau at higher metal concentrations, corresponding to multilayer mechanism.

Methyl orange and methylen blue are two dyes resulted from the textile industry. They are not raising just esthetical problems, but they are toxic and hence harmful to aquatic animals. The aim of this study is to test the capacity of three types of sawdust (oak, willow and white poplar) and mixed substrates, sawdust: fly ash (FA), to remove the methyl orange (MO) and methylen blue (MB) from wastewater. The influence of contact time, solution pH and initial concentration of dyes on the bleaching efficiency was investigated. Sorption kinetic data were fitted to the pseudo-second-order model. Adsorption isotherms were investigated to completely understand the adsorption processes. The adsorption isotherm data were best fitted by the Freundlich isotherms in most cases. The kinetic and thermodynamic results outline the important role played by the substrates porosity and the dyes type, particularly the dyes volume. The results indicate the all substrates, sawdust and sawdust: FA can be used as an efficient and lowcost alternative for removal of the dyes from wastewater.

This paper presents the results obtained in copper removal from wastewater by using sawdust and mixtures of fly ash and sawdust. The adsorption efficiency of the copper ion from 0.01m solutions was tested on mixtures with various waste components ratio and the results are compared with those obtained on single substrates. Three types of sawdust, oak wood, (Querqus robur), white poplar, (Populus alba), and willow, (Salix alba l.), were pre-treated to optimize the sawdust affinity for heavy metals adsorption and for increasing the fly ash affinity for copper adsorption. The adsorption parameters were optimized (contact time, amount of substrate for 100mL solution) and further used for identifying the optimal heavy m/sorption efficiency on willow; willow: FA-W and willow: FA-A.