The figure on the left represents the sample at the start of the experiment, and the figure on the right shows the sample after the experiment has been carried out. (Graphic courtesy of UPES)

?A new study by scientists at the University of Petroleum and Energy Studies, New Delhi, India, has revealed a greener method to reduce total dissolved solids (TDS) in water. The study’s goal was to assess the suitability of a method for water treatment, used in rural areas of developing countries such as India, to determine its applicability to onshore U.S. water produced from coalbed-methane (CBM) drilling.


CBM wells produce more water than conventional reservoirs. Water is removed by pumping to help lower the reservoir pressure, which stimulates desorption of methane from the coal.


When produced water is disposed as is into the environment, it is believed to create groundwater depletion, groundwater contamination through the presence of methane in the ground water, and degradation of existing surface water due to mineral content. Dissolved solids, electrical conductivity and sodium adsorption ratios must be monitored before the disposed water is put to re-use.


The study found an improvement of water quality from direct filtration using organic seeds as a coagulant, and focuses on achieving purification using minimum energy resources.


In this case study, based in India, CBM waste­water pumping and disposal was incurring high costs depending on the particular well’s depth and stimulation type. The total water-disposal cost was about $1 to $4 per barrel, due to pipeline maintenance, repair costs, electrical costs to operate pumps, virtually around-the-clock staffing to operate electrical generators, longevity of the facility, injection-well depth and chemical treatments used to disinfect the water for re-used by livestock.


A one-liter sample was taken and loaded with a solids content of 5,000 parts per million (ppm) of TDS. Two seeds of strychnos potatorum, a yellow circular seed from a deciduous tree found in India, were added to the solution and left undisturbed for 96 hours. The experiment was conducted at room temperature and atmospheric pressure. After four days, a sample was collected from the jar. The TDS was reduced to below 1,000 ppm.


The seeds contain naturally occurring polyelectrolytes, which can be used as a coagulant to clarify turbid water. In other laboratory tests, direct filtration of turbid surface water through the seeds produced a substantial improvement in its aesthetic and microbiological quality.
The chemical composition of the coagulant in Strychnos potatorum suggests that the seeds function as a particulate, colloidal and soluble polymeric coagulant as well as a coagulant aid. While these natural coagulants produce low-risk water, additional disinfection or boiling may be needed to bring the water to potable standards.


There are several advantages to this process. In India, the method’s cost is low because the seeds’ cost is small when compared with other methods. It can be used in rural areas where technology and trained workers are difficult to obtain. It does not require any energy for purifying the produced water, is applicable to oilfield water and does not involve high pressure and temperature.


However, there are disadvantages. The applicability is limited to the availability of the container materials and seeds in large quantities to carry out the process on a commercial scale. Also, it is a slow process requiring retention time for the coagulants to separate the dissolved solids from water. Finally, as it cannot reduce the concentration of the dissolved solids to minimum ppm values, it is recommended for use as one of several processes to carry out multi-stage operations for purification.


More research is needed to define, optimize and standardize conditions for this method. More effort is needed to encourage and disseminate the water-treatment method to determine its acceptability, sustainability, cost and effectiveness in reducing waterborne, infectious diseases.


Other CBM wastewater solutions include injection into aquifers depleted by CBM production, discharge of water into tanks to be trucked out, or discharged-into-surface flows, such as sewage canals, for improved stream flow with adequate mitigation. Further solutions include using produced water in various industries, such as coal mining, dust-depression operations for roads, enhanced oil recovery and for cooling towers.

--Based on a study by Sanjay Surya Yerramilli and Rameshchandra Yerramilli.

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