Wastewater samples of varying strength was synthesized and removal efficiency was analyzed for variation with respect to pH, contact time, mushroom size, strength of copper solution and mushroom dosage. Synthetic stock solution was prepared by dissolving appropriate quantity of analytical grade chemical in distilled water.
The procedure for the same and that of colorimetric analysis of copper was referred from Standard methods (APHA, 1995). The experiments were carried out under steady-state and stirring conditions, and residual concentration analysis was conducted at an interval of every 30 minutes. The absorbance of the blue color developed was measured at 620nm using a Photoelectric colorimeter (Figure 2).
RESULTS AND DISCUSSION
Effect of pH on removal efficiency
Copper removal by milky white mushroom was initially carried out at a varying pH of 1 to 4. The pH profiles usually vary with different heavy metals, as each heavy metal shows potential for maximum sorption only over a specific range. For copper, the tests yielded best results at a pH of 3.5. The chief cause for better adsorption at low pH may be attributed to the presence of large number of H+ ions, which in turn, neutralize negatively charged adsorbent surface, thereby reducing the interference to the diffusion of metallic ions. At higher pH, the reduction may be attributed to OH- ions, creating increased hindrance to diffusion. Further attempts, for higher pH values resulted in the precipitation of copper as copper hydroxides.
Effect of strength of copper solution on removal efficiency
As the initial concentration of copper solution was increased from 5.09mg/ml to 25.46mg/ml, a decline was observed in the removal efficiency from 30.75% to 20.15%. This is because as the solute concentration increases, it reduces the availability of pores for all the solutes.
Effect of contact time on removal efficiency
It was observed that the rate of uptake of Cu2+ was rapid initially and slowed down in the later stages. As the detention time varied from 0-90 minutes, the removal efficiency increased up to 30%. However, during the interval of 90210 minutes, the efficiency reduced to 25.50%. The percentage removal is higher in the initial stages, as adequate surface area of mushroom is available for physical adsorption. As a result, the rate of uptake is faster. As time elapses, some of the active sites are blocked, hence the rate of uptake becomes slow in the later stages. Analysis for 24 hours residual concentration yielded an efficiency of 25%, indicating no significant uptake by the mushroom. Hence, it can be concluded that the rate of adsorption and de-sorption of heavy metals by Calocybe indica remains marginal after 210 minutes.
Effect of Mushroom size on removal efficiency
‘Milky White Mushrooms’ were generally categorized as small, medium and large for this test. While the percentage removal of copper increased from 11.25% for small size, to 25.50% for medium size, it was observed to be greatest by 30.75% for large sized mushrooms. The results are so found, since the large sized mushroom provides a greater surface area for heavy metals to get adsorbed.
Effect of Dosage of mushrooms on removal efficiency
When the mushroom dosage was increased from 10 gm to 100gm, the removal efficiency increased from 12% to 35.65%. The findings clearly indicate an increase, since greater dosages raises the numbers of pores for entrapment. For this test, the mushrooms were cut into fine slices to achieve a greater surface area while ensuring the structure isn’t disintegrated.
Effect of Stirring conditions on removal efficiency
All the previous studies were carried out under steady-state condition. The final setup analyzed the impact of stirring conditions on the adsorption process. Under stirring condition, the removal rate by milky white mushrooms was found to be 42.15% as depicted in Chart 1. This is comprehensively an edge over the steady conditions, where the efficiency was found to be 30.75%. As Van-der-Waal’s forces are greater in stirring condition, the artificial forces generated are greater than in idle condition, hence, the rate of movement of ions into pores also varies, thereby aiding in Adsorption process.
From the Freundlich isotherm plot (Chart 2) for x/m vs. Ce, Kf is found to be 0.005 and n as 8.28. The range for n is 2-10, therefore 8.28 indicates good adsorption. Langmuir isotherm was not applicable as there was no formation of any linear curve and since a curvilinear plot was obtained.