Experimental investigation of an effective solar hybrid system for treatment of concentrated brine solution of desalination plants

Abstract

Desalted water and highly saline water (brine discharge) are two main primary streams produced by desalination plants. The disposal of brine into the sea in the case of coastal desalination plants, or in the groundwater aquifers in the case of inland plants caused harmful effects on the environment. It can adversely affect the ecosystem of the sea animals in addition to increasing the water salinity of the aquifers. Therefore, the brine produced from RO desalination plants under high pressure (plants without an energy recovery system) is utilized to operate a turbine coupled with a generator to generate energy, which is used as an energy source for MD pumps. In addition, the brine passed through the solar collector is used as a pre-heating to achieve the acquired temperature for evaporation in the membrane distillation device. Moreover, the produced highly concentrated saline solution will be evaporated using an evaporation pond (EP) and a byproduct is produced in the form of salt that can be separated into several types to be used in the industry. It found that the system is economically visible by decreasing the cost of the desalted water and increasing the quantity of fresh water through condensing the evaporation produced from the MD and evaporation ponds. The RO system with 28 l/min feed water inlet, produce 6 l/min permeate water and 22 l/min brine water. For unit area of MD and EP (1 m2), the amount of fresh water recovery from brine water is 0.62 l/min which represent 3% recovery. This percentages proportionally increased to 28%, 70 % and 98% by increasing the surface area of the MD and EP to 10 m2, 25 m2, and 35 m2 respectively. It is found that the current experimental work achieved gained output ratio GOR values ranging from 0.18 to 0.66 which comply with the range of the previous researches. In addition, the maximum water flow (25 l/min) produces a higher rotational speed in the generator. The rotational speed also increases with the increasing of nozzle diameter from 1 mm to 6 mm and then decreased with a nozzle diameter larger than 6 mm. The presented system is considered one of the positive contributions to the environmental protection program.