الفهرس 
Wastewater and PollutionOnly 14 pages are availabe for public view
Abstract
Not be considered remnants of laboratories working with a academic institutions and industrial (Schools - Institutes - Universities - factories) in the habit of the main sources of environmental pollution. Although these wastes contain hazardous substances harmful to the environment and are produced on a regular basis, and being discharged without treatment in the sewage networks.
Laboratory applications in some labs of university faculties in Libya suffer from non-availability of practical procedures concerning environment protection based on proper bases. In such environments, lots of chemical substances are consumed periodically. Regarding the increasing size and quantity of these wastes with their different kinds and forms (gaseous – liquid – and solid) and as a result of the increasing numbers of experiments being administered in labs for the increasing numbers of students. Human industrial and urban waste water containing which Heavy metals, were discharged into sewage systems, caused a serious problem that is a major concern worldwide. Many experiments were designed focusing solely on learning objectives, and therefore many of them unnecessarily produce a considerable volume of polluted wastes including heavy metals that must be properly handled and disposed. Wastewater treatment in universities is facing new challenges as heavy metals removal becomes necessary due to the requirements of laws and regulations.
Research Objectives
The main objective of this work is to investigate the possibility of treating liquid waste generated from experiments of inorganic chemistry laboratory to remove heavy metals before discharging into public sewerage network.
Research Methodology
The study begins with reviewing relevant research and studies. In the second stage of the study that covers the applied part and prepare synthetic solution by spiking distilled water with different metal salts to achieve the desired metal concentration. All chemicals used were of analytical grade. The chemicals used are copper sulfate (CuSO4. 5H2O), lead nitrate Pb(NO3)2, cadmium chloride (CdCl2.H2O), potassium permanganate (KMnO4), nickel chloride (NiCl2.6H2O), cobalt Chloride (CoCl2), potassium chromate (K2CrO4), silver sulfate (AgSO4) and potassium aluminum sulfate K2Al2 (SO4)4. The solution was prepared by dissolving 1g of each metal salt in 6 liters of distilled water.
All experiments were carried out in bench scale and this study was conducted in three different phases, phase I, phase II and phase III.
In phase(I),experiments were conducted with single precipitating agents, sodium hydroxide, calcium hydroxide, sodium sulfide or calcium carbonate were added to the liquid waste at different pH values, and then allow it to settle. While sequential precipitation was performed in phase (II) where more than one precipitates agent used sequentially precipitation. In the sequential precipitation the pH of liquid waste was adjusted at different values using sodium hydroxide or calcium hydroxide then allow for settling then sodium sulfide or calcium carbonate was added to the settled water and then allowed to settle. The reduction of chromium precipitating was used in phase III 2 precipitates agents were used sodium sulfite is added to the synthetic solution and the pH is lowered to 3.0 or less using acid (typically sulfuric acid). This process converts chromium from the hexavalent form to the trivalent form. The trivalent form can be treated similar to other metals and the pH of Liquid waste was adjusted at different values using calcium hydroxide then allow for settling.
Collected water samples were analyzed for metal concentration using atomic absorption spectrometer (AA-600, PerkinElmer, USA) according to the Method in Eaton (1998). pH of the Liquid samples were analyzed by using METTLER TOLEDO S2a’0p-k pH meter with a glass electrode. Jar test-apparatus Phipps & Bird stirrer model were used to mix the wastewater with the added metal solutions.
RESULTS AND DISCUSSIONS
Heavy metals removals
Chemical precipitation is widely used for removal of heavy metals from inorganic wastewater effluents. After adjusting the pH of the wastewater, or adding chemical agents the dissolved metal ions are converted to insoluble form through a chemical reaction with the precipitating agent.
The best treatment of each technique was evaluated by comparing the concentration of total metals remaining after applying different treatments in each technique.
The remaining concentrations for each element in the liquid samples were compared with the regulatory limits. These comparisons were carried out for the best treatments in each technique.
CONCLUSIONS
In this study, three techniques of liquid waste treatment were used to reduce the concentration of heavy metals in laboratory wastewater. These techniques are single precipitation, sequential precipitation and reduction of chromium and treatment precipitation.
Compared with the other techniques the single precipitation of heavy metals using sodium sulfide at pH7 was recommended for the removal of heavy metals from liquid waste of laboratories of inorganic chemistry. This techniques was able to remove Cu+2, pb+2, Cd+2, Mn+2, Ni+2, Co+2 , Cr+6 ,Ag+ and Al+3 at efficiencies of 99.999%, 99.99%, 99.96% 99.87%, 99.89%, 99.95%, 99.97%, 99.99% and 99.84% respectively. The remaining concentrations of these heavy metal elements in liquid waste after treatment were below the limits of the Egyptian law 93 for the year 1962 and the Libyan law 1 for the year 2008 and Ministerial Decree 44 for the year 2000 regarding the disposal of liquid waste into municipal sewers. The technique is simple and easy to operate provide high removal efficiency low cost and produce small amount of sludge.