Valorization of Some Untreated Low Cost Adsorbents for Water Pollution Control

The present article describes the adsorption behavior of some low cost adsorbents such as olive waste, maize cobs, bentonitic clay, wheat bran, coal ash and coffee waste, with respect to Pb2+, Cu2+ and Zn2+ ions. The batch method was used and parameters such as electrical conductivity, pH, contact time, adsorbent dosage and initial and final concentration of metal ions were studied. All used adsorbents were effective, but coal ash was most effective, with total removal for all ions of over 90%, with highest percentage removal from 99.2% for Zn2+ ions and 97.5% of Pb2+. Maize cob was an effective adsorbent with maximal percentage removal of 92.6% for Zn2+ ions, wheat bran had highest removal of 93.7% for Pb2+ ions as did olive waste, 97% for Pb2+ ions. Coffe waste offers considerable promise as a low-cost natural adsorbent with highest efficiency in removal of Pb2+ with 97.5% while bentonitic clay having a structure with net negative charge, which is neutralized by positively charged species, resulted also as an effective low cost adsorbent with max total removal from 92.7% for Pb2+ to 80.9% for Zn2+ ions. keywords: olive waste; maize cobs; bentonitic clay; wheat bran; coal ash; coffee waste;

keywords: olive waste; maize cobs; bentonitic clay; wheat bran; coal ash; coffee waste; inTrOdUCTiOn Through history, quality and quantity of water that was at human disposal, was a decisive factor for determining their welfare.At one time, clean fresh water supplies were considered inexhaustible.
Only recently have we begun to understand that we will probably exhaust our usable water supplies and this can be directly attributed to human abuse in the form of pollution.Industrial activity alters the natural flow of materials and introduces novel chemicals into the environment which effluents contain toxic substances especially heavy metals, dyes, phenols, etc., 1 .Some heavy metals are necessary in small amounts for normal development of biological cycles, however most of these heavy metals are becoming toxic at high concentration 2 .Polluted water is aesthetically objectionable for drinking, irrigation, industrial activities and other purposes 3 as pollutants alter physical, chemical and biological properties of water, hence affect human health and ultimately ecosystem.Different methods (adsorption, electrolytic or liquid extraction, electro dialysis, chemical precipitation, membrane filtration) have been developed for decontamination of industrial waters 4,5,6,7,8 .From all methods used, adsorption has been found to be superior to other techniques for purification of water in flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants 9,10,11,12,13 .When comparing the adsorption materials, one must have in mind cost as a very important parameter.However, an adsorbent can be assumed as low cost if it requires little processing, is abundant in nature, or is a byproduct or waste material from another industry.Some biosorbents can bind and collect a wide range of heavy metals with no specific priority, whereas others are specific for certain types of metals 14 .Different low cost adsorbents have been used for wastewater treatment, some more effective than others 15,16,17 .Activated carbon is usually derived from natural materials (biomass, lignite or coal) and has been a popular choice as an adsorbent for long time 18,19 , but its high cost poses an economical problem.Different authors tried different low cost adsorbents like clays 20 , microbial and plant derived biomass 21 , chitin and zeolites 22 , sawdust 23 , rice husk 24 , soybean hulls 25 , sugarcane bagasse 26 , etc.
In the last decade, olive oil production has increased by approximately 40 % worldwide and this implies a proportional increase in huge quantities of liquid and solid wastes.Double-fold advantage, with respect to environmental pollution, is to use such solid wastes and to convert them in inexpensive adsorbent for water pollution control.This way a part of solid waste material could be reduced, and the developed low-cost adsorbents can treat industrial wastewaters at a reasonable cost 27,28,29 .Solid residues from corn production such as corn cobs can also be used as raw materials in the production of adsorbents 30,31 .Wheat bran, another agricultural waste was studied for its adsorbent properties 32,33 .In recent years there has been increasing interest in studying also natural waste materials that arise from food industry, e.g.coffee waste 34,35 those that come through various industrial processes, like coal ash 36,37 and other natural low cost materials, like bentonitic clays 38,39 .
In present study we've analyzed some low cost materials, olive waste, maize cobs, bentonitic clay, wheat bran, coal ash and coffee waste as potential adsorbents for removing of Pb 2+ , Cu 2+ and Zn 2+ ions from standard solutions.

Adsorbent
The starting materials, maize cobs, wheat bran, and coffee waste were obtained commercially from Kosovo, coal ash was obtained from Thermo Power Plants in Kosovo, bentonitic clay from Vitia, Kosovo while olive waste were obtained from olive oil industry in Ulqin, Montenegro.All the adsorbent used where sieved and dried at 105ºC to a constant weight.
In terms of physical-chemical properties, chemical composition of ash varies greatly, depending on the type of coal and its origin.Coal ash from our lignite type coal (Thermo power plants Kosova A and B) has specific inorganic composition with predominance of alkaline components (CaO and MgO), while bentonitic clay although also alumosilikate, has predominance of acidic constituents (SiO 2 ).Adsorbents of agricultural origine have high mechanical strength, rigidity and porosity and they have polymeric groups like cellulose, hemi-cellulose, pectin, lignin and proteins as active centers for metal uptake 40 .

General procedure for adsorption studies
The sorption of Pb 2+ , Cu 2+ and Zn 2+ ions on used adsorbents (olive waste, maize cobs, bentonitic clay, wheat bran, coal ash and coffee waste) was studied using a batch technique.The general method used for this study is described as follows.The stock solution of PbSO 4 , CuSO 4 and ZnSO 4 at a concentration of 10 mg/L was used in all experimental runs.A known weight of adsorbent (1g and 5g) was equilibrated with Pb 2+ , Cu 2+ and Zn 2+ solutions of known concentrations in a stopped pyrex glass at a fixed temperature in a thermostatic shaker bath (300 rpm) for a known period of time (30 min and 60 min).After equilibration, the suspension was filtered and analyzed with AAS.

reSULTS And diSCUSSiOn
Since heavy metals are natural components of the Earth's crust and they cannot be degraded or destroyed, their treatment is of special concern due to their recalcitrance and persistence in the environment.Manufacturing a diversity of adsorbents as raw materials is being studied (olive waste, maize cobs, bentonitic clay, wheat bran, coal ash and coffee waste) since these materials are renewable, usually available in large amounts and less expensive than other materials to.Use of waste materials as inexpensive adsorbents for removing of heavy metal ions from water and wastewater presents a great contribution in the reduction of costs for waste disposal, therefore contributing to environmental protection.
The sorption of Pb 2+ , Cu 2+ and Zn 2+ ions on used adsorbents was studied using a batch  technique.Concentration of heavy metal ions before treatment was 4 mg/dm 3 for Pb 2+ ions, 3.57 mg/ dm 3 for Cu 2+ ions and for Zn 2+ ions it was 4.98 mg/ dm 3 , respectively.pH of these untreated aqueous solutions were 5.29 for Pb 2+ ions, 6.0 for Cu 2+ ions and for Zn 2+ ions pH was 5.4, respectively.Electrical conductivity for all heavy metal ions before treatment was 0.00 µS/cm.Results of treatment of each heavy metal aqueous solution with used adsorbents are given in Table 1.
From the results shown in Table 1 it can be noted that pH of aqueous solution of Pb 2+ , Cu 2+ and Zn 2+ ions after treatment with maize cobs, olive waste and wheat bran are almost the same as they were before treatment, while after treatment with coal ash pH are increased from8.3 to 11.3 due to predominance of alkaline components in our coal ash, while after treatment with bentonitic clay and coffee waste pH are slightly lower from 4.03 to 6.3, due to their acidic nature.Electrical conductivity of aqueous solution of Pb 2+ , Cu 2+ and Zn 2+ ions after treatment with all used adsorbents was slightly increased from 0.01 µS/cm to 5.15 µS/cm when 5g of adsorbents were used.Adsorbent dosage is an impor tant parameter because this determines the capacity of an adsorbent for a given initial concentration of the adsorbate.The effect of adsorbent (olive waste, maize cobs, bentonitic clay, wheat bran, coal ash and coffee waste) dose on the adsorption of Pb 2+ is presented in Figure 1a.As shown in this figure, results of percentage removal of Pb 2+ ions are very high with all adsorbent used, ranging from 87.5% for maize cobs to 97.5% for coal ash and coffee waste.From this figure it can be noted that there is no significant impact in precentage removal of lead with the increase in adsorbent dosage from 1g to 5g.Slightly greater removal of lead is noticed with olive waste, 6.2%, while with maize cobs 2.2%, wheat bran 1.8% and bentonitic clay 0.8% the impact was very small.Coal ash and coffee waste demonstrated no effect when adsorbent dosage was increased.
Figure 1b shows the effect of contact time on percentage removal of Pb 2 .It was observed that percentage removal slightly increases with contact time.Highest increase in percentage removal was observed with olive waste, 7.3% or bentonitic clay showed 2.5% increase in percentage removal with increase in contact time from 30 min to 60 min.Coal ash and coffee waste did not show any effect with increase of contact time.
Figure 2(a) shows the effect of adsorbent dose (1 and 5 g/dm 3 for 30 min) on the adsorption of Cu 2+ ions.From these results it can be noted that coal ash was best adsorbent for removal of Cu 2+ with 98.9% of removal while wheat bran removed 52.7%.Increasing adsorbent dose from 1g to 5g had more effect on removing of Cu 2+ ions, e.g., adsorption on olive waste increased for 10.2% while with wheat bran increasing in percentage removal was 5.3%.Other adsorbents showed small increase for fivefold increase in adsorbent dosage, while coal ash showed no effect in percentage removal of Cu 2+ ions.
The effect of contact time on percentage removal of Cu 2 is shown in Figure 2 10.2% and wheat bran 7.6%, while bentonitic clay and maize cob showed 6.4% and 5.3% respectively.Coal ash did not show any effect with increase of contact time.
Figure 3(a) and 3(b) shows percentage removal of Zn 2+ ions from all used adsorbents.Figure 3(a) shows results of percentage removal of Zn 2+ after treatment with all adsorbent dosage of 1g and 5g for 30 min of contact time.It can be noted that adsorbent dosage had most effect in bentonitic clay, increasing percentage of removal for 13.3% with increasing of dosage for fivefold.Smaller impact was noted with olive waste 8.1%, maize cobs 5.8%, coffee waste 3%, wheat bran 1%, while coal ash showed no impact at all.Both graphs also confirms that most effective adsorbent on removal of Zn 2+ was coal ash with over 99% of total removal and least effective was wheat bran with 80% of total removal.Figure 3(b) shows that percentage of removal of Zn 2+ ions in dependence of increasing contact time, from 30 min to 60 min, did not have any effect in coal ash, had a small effect in coffee waste 1.6%, 3% in bentonitic clay, 5.8% in olive waste, 7.9% in wheat bran and highest effect was noted for maize cob with 8.7% increase.

COnCLUSiOnS
The present study shows that all adsorbents used were an effectual biosorbents for removal of Pb 2+ , Cu 2+ and Zn 2+ ions from aqueous solution.Maize cob was an effective adsorbent with maximal percentage of removal of 92.6% for Zn 2+ and 66% for Cu 2+ ions.Wheat bran was also effective adsorbent for highest removal of Pb 2+ with 93.7% and lowest percentage of removal for Cu 2+ with 52.7%.Another adsorbent that showed good sorption properties was olive waste, with highest removal from 97% for Pb 2+ and lowest percentage removal for Cu 2+ from 62%.Our preliminary results indicate that coûee waste oûers considerable promise as a low-cost natural adsorbent.Highest efficiency was noticed in removal of Pb 2+ with 97.5% while lowest percentage removal was noticed for Cu 2+ with 91%.Bentonitic clay having a structure with net negative charge, which is neutralised by positively charged species, resulted also as an effective low cost adsorbent with max total removal from 92.7% for Pb 2+ to 80.9% for Zn 2+ .Most effective adsorbent that we used was coal ash with total removal for all ions over 90%, with highest percentage removal from 99.2% for Zn 2+ ions and 97.5% of Pb 2+ .For all adsorbent used adsorbent dosage and contact time did not have significant impact in their adsorption capacities.As conclusion all these agro and industrial waste materials, to overcome environmental pollution, are low cost, eco-friendly and easy alternative instead of using chemicals for the removal of heavy metals and other pollutants.