Recovery of Silver and Mercury from COD Waste

Chemical Oxygen Demand (COD) is an important parameter for determining the pollution potential of domestic and industrial wastewater. During the course of its analysis, silver sulphate is added as catalyst while mercuric sulphate is added to overcome the interference from halides. After analysis, the COD waste containing the compounds of silver and mercury are disposed off. Considering the hazardous nature and cost factor, an effort was made to recover silver as metallic silver and mercury as mercuric iodide.

The COD waste was treated with dilute HCl to precipitate silver as silver chloride. The silver chloride was dissolved in dilute ammonia and sodium sulfide was added to precipitate silver as silver sulfide. The silver sulfide was mixed with flux material and ignited to 1200 ⁰C to separate silver metal and slag material.

The waste after recovery of silver, contains mercury in its compound form. Potassium iodide can precipitate mercury as mercuric iodide. But excess addition of potassium iodide will dissolve the precipitate. Hence, calculated amount of 10% potassium iodide was added to precipitate all mercury as mercuric iodide.

As much as 18 grams of silver were recovered from 15 litres of COD waste. The recovery percent for both silver and mercury was found to be more than 95%.

Analytical Quality Control (AQC/Water) for the Laboratories of Pollution Control Boards/Committees and EPA Recognised Laboratories

Analytical Quality Control (AQC) is one of the main tools by which the performance of a laboratory can be assessed in terms of accuracy and reliability of analytical data generated by the laboratory.             The Central Pollution Control Board is monitoring 507 water quality monitoring stations under GEMS, MINARS, GAP and YAP  Programmes comprising rivers, lakes, wells, and ground waters spread over 23 states and 5 Union Territories through various State Pollution Control Boards.  In order to obtain reliable and accurate analytical data, CPCB had started regular and organized Analytical Quality Control (AQC) exercise for laboratories of SPCD/PCC, E.P. Act recognized laboratories Under this project, 8^th rounds of AQC exercises covering 21 physico-chemical parameters were carried out for 109 laboratories during 2001.  The year wise growth in terms of number of participating laboratories under the scheme is presented In Figure below.

The overall performance of the laboratories was assessed with respect to following parameters.  Ammonical Nitrogen, Chloride, Chromium, Calcium, Boron, Total Hardness, Potassium, Total Dissolved solids, Conductivity, Chemical Oxygen Demand, Sodium, Magnesium, Fluoride, Sulphate,  Total Kjeldahl Nitrogen, Nitrate-N,  Biochemical Oxygen Demand, Fixed Dissolved solids, Total Suspended Solids, Phosphate-P, pH .

Development, Standardization and Preparation of AQC Samples for Total Coliform and Faecal Coliform for Conducting AQC Exercises

CPCB is conducting AQC exercises covering various physico-chemical parameters. In the AQC exercises, bacterial parameters like Total Coliform and Faecal Coliform are not yet included because of constraints in preparation of bacterial AQC samples and their preservation and despatch under ice-cold condition.  To overcome these problems it was decided to prepare lyophilized bacterial samples in solid form like the one developed for BODSEED in collaboration with the Centre for Biochemical Technology(CBT), CSIR, Delhi. The main objectives of the proposed project are:

Ø      To introduce the bacteriological parameters like Total Coliform and Faecal Coliform in AQC scheme;

Ø      To improve the analytical efficiency of concerned laboratories with reference to bacteriological parameters; and,

Ø      To get accurate and reliable data on total coliform and Faecal coliform.

The microbial samples developed were tested in CPCB laboratory to assess the precision and accuracy of the test results.  It is planned to introduce  Bacterial samples in AQC Inter-laboratory Proficiency Testing (PT) programme in the forthcoming exercises.

Development of Certified Reference Material (CRM) of Toxic Metals using Industrial Effluents

The need for accurate analytical measurements of metals during environmental monitoring is well recognized and accomplished with use of reference material. Standard Reference Materials (SRM`s) are well characterized materials used to maintain the quality of measurements.  The use of Certified Reference Material (CRM) during routine measurement of trace metals is expensive. Therefore, it has become necessary to develop economical and indigenous Certified Reference Material (CRM). CPCB has undertaken a project for preparation of Reference Materials for toxic metals in industrial effluents under sponsorship of the Department of Science & Technology (DST). 

The Certified Reference Materials for toxic metals like Chromium Copper and Nickel in Electroplating industrial effluent were selected and the homogeneous samples were distributed to 32 reputed environmental and R&D laboratories in the country for analysis.  The analytical data as obtained from 32 laboratories have been compiled, statistically analysed and computed in order to certify its use as reference material. The statistically processed data are graphically presented ahead:

Development and Standardization of Soil and Solid Waste Analysis for Analytical Quality Control (AQC)

A project was taken up to standardize the analysis of soil (polluted) and solid waste with a focus on conducting AQC exercises to the laboratories of SPCB/PCC and also laboratories recognized under E.P Act. In this project, different polluted soil, industrial solid waste, Hazardous wastes and Municipal Solid Waste are to be analysed.

Samples of Municipal Solid Waste (MSW) from New Delhi Municipal Corporation Compost plant were collected, homozinised and analyzed for various physico chemical parameters and standardization of methodology was completed. The analytical procedure will be provided to all the laboratories for developing the analytical facilities. After fulfilling the preliminary requirements, AQC samples of these types of waste will be distributed and Inter laboratory Proficiency testing will be conducted in phased manner. The outcome of the project work will be helpful in development of the facilities for analyzing solid wastes for various laboratories of SPCB/PCCs and to improve the analytical capabilities.

Monitoring of Ground Water Quality around Municipal Solid Waste (MSW) Disposal Sites in Delhi

Delhi is one of the largest Municipal solid Wastes (MSW) generating cities. The quantity of wastes is more than 7000 metric tonnes per day.  The wastes are disposed mainly on land at three landfill Sites (LFS), namely Ghazipur (East), Okhla (South) and Bhalswa (North). The wastes include mainly organic materials (60%) obtained from various sources like domestic, vegetable markets, hotels, commercial areas etc. These sites are not provided with any lined materials for avoiding percolation of leachate from the solids and possibility of contamination of groundwater. In order to estimate the levels of groundwater contamination in these localities, a project on the monitoring of ground water quality around solid waste disposal sites in Delhi has been taken up.

Two rounds of groundwater samples numbering 31 in around the three sites have been collected and analyzed for various physico-chemical parameters (23) including heavy metals (9), pesticides (5), and bacteriological parameters (2). One round of Air borne microbial counts (Total Coliforms and Fungi) was also carried out in November, 2001. The outcome of the project work will be helpful for assessing the impact of MSW sites on Ground water quality, air quality, air borne microbial organisms and to formulate strategic plans for selecting MSW land fill sites.

Technology Development of Specific Microbial Packages for Treatment of Paper & Pulp Industrial Wastewater

The efficiency of treatment of industrial wastewater depends upon the composition of chemicals and their reaction with microbial action on the wastes.  There are specific groups of bacteria, which act effectively with specific types of waste and degrade the waste in a fast and efficient manner.  Keeping this fact in view, a project was taken up in collaboration with the Centre for Biochemical Technology (CSIR), and Delhi with sponsorship from the Department of Biotechnology, New Delhi.  

Samples from Paper mill were collected and analyzed and characterization has been made for screening the suitable and efficient bacterial composition.  Trial runs were made to find out the degradation rate of the microbial package using the effluent. The outcome of the project work will be helpful in development of special microbial package which will treat the paper & pulp wastes in effective manner in terms of time and pollutants like BOD, Lignin, colour, AOX, TDS etc.