Chapter 1
Tackling Challenging Industrial Separation Problems through Membrane Technology

Siddhartha Moulik1,2, Sowmya Parakala1 and S. Sridhar1,2,*

1Membrane Separations Group, Chemical Engineering Division

2Academy of Scientific and Innovative Research (AcSIR), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad, India - 500007

*Corresponding author: sridhar11in@yahoo.com

Abstract

Membrane processes such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) for water and wastewater treatment have been developed, and widely used over the past few decades with proven efficiency. Currently emerging membrane techniques such as i.e., pervaporation (PV), vapor permeation (VP) and membrane distillation (MD) are being developed since they portray high potential with additional advantages and minor limitations over the conventional processes, and are thus regarded as next generation technologies. These processes can easily be retrofitted with existing conventional treatment methods for drinking water purifications, domestic, municipal and industrial wastewater treatment. The fundamentals of water resources available and their contamination, water and wastewater and their conventional treatment techniques, and the limitations of first-generation membrane technologies will be discussed in this chapter. The main focus is on technologies which are low cost and energy efficient, and provide high yield and desired purity with minimal sludge. The potential of second-generation membrane processes, i.e., PV, VP and MD has been explored and showed promising results by fulfilling all the ideal characteristics of next-generation membrane separation processes.

Keywords: Membrane technology, water/wastewater treatment pervaporation, vapor permeation, membrane distillation

1.1 Water: The Source of Life

Water has become the 'mother' and 'matrix' of life, essentially interlinked with the existence of biological lifecycles. Water is certainly the most precious natural resource that exists in the universe for human consumption. Water on the earth is available mostly as salt water (97.5%) with the remaining 2.5% being fresh water [1], which can be further distributed into 0.3% in lakes and rivers, 30.8% groundwater including soil water, swamp water and permafrost, and 68.9% as glaciers and permanent snow covers. Only 30% of the total fresh water resources are easily accessible to humans (as lakes and streams), which is shown in Figure 1.1. This raises a question on whether there will be enough fresh water available for future generations. Hence, there arises the need to make the fresh water resources sustainable; through recycle and treatment of wastewater, desalination of sea and brackish water, purification of contaminated groundwater and surface water for making them safe for drinking or utilization as process water. This chapter discusses the technologies required for drinking water purification and effluent treatment using first and second generation membrane separations.

Figure 1.1 Distribution of water on the earth.

The total mass of water on the earth is constant in its different phases such as ice, atmospheric water, clean water and ground water. The overall hydrologic cycle is a conceptual model that undergoes storage and movement of water between the biosphere, atmosphere, lithosphere and the hydrosphere. There is no starting point for the water cycle. Since three-fourth of the earth's surface is occupied by water, it will be wise to initiate its cycle from the oceans. Water gets warmed up in daylight and evaporates. Some water gets directly sublimated from the glaciers and icebergs and rises upward. At higher altitude, the gradual decrease in ambient temperature and pressure make the vapors supersaturated and they get condensed, forming clouds. The clouds roam miles across the earth and finally at a supersaturated state, fall in the form of rain, snow, hail, dew, frost or sleet over the Earth. Water is distributed in nature in different forms such as rain, river, spring, mineral water and seepage water, which get stored in different natural reservoirs such as atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields and ground water table [2]. Water is not only vital for sustenance of life, but also essential for socio-economic developments such as agriculture, industry, energy production, transportation, etc. The rapid industrialization and urbanization would have been scarcely possible without adequate supply of water. Renewable surface and ground water are the natural resources recognized to meet the increasing demands of society. With increasing population and exploitation of natural resources for one's own benefit, mankind has behaved in a wild manner by creating problems of pollution which are hazardous to life as well as aquatic flora and fauna. To combat water pollution, we must understand the sources and problems from the grassroot stages to be a part of the solution.

Water is the major requirement for a healthy life. Keeping water sources free from pollution is of utmost importance in the drive towards water conservation. Polluted water is the major source of diseases, and the land also becomes unfit to sustain life. At present, the potable water consumed by 80 to 90% of the population is of poorer quality by international standards and 2.1 billion people lack access to safely managed drinking water services [3]. Thus, the source of water available to humans is much lower than the 1% present in lakes, streams and underground. Misuse, pollution of water bodies and uncontrolled growth of human population further strain this limited resources. Surface water can be found on the land in the form of streams, ponds, marshes, lakes or other fresh (not salty) sources. Rivers are the main source of surface water and as many as 13 rivers in India are categorized as major sources of surface water with a catchment area around 252.8 million hectares. Surface water as reported by CPCB [4] from 120 rivers contains toxic metals. Toxic metals like arsenic, copper, chromium, nickel, mercury and lead were found to be present in rivers mostly in permissible limits except for few. CPCB has identified 1145 industries in the country that pollute river bodies. Ground water is found underground in the sweeps and spaces, soil, sand and rocks. A global scenario of ground water usage is represented in Figure 1.2. Current status of ground water in India is shown in Table 1.1 [5]. It is stored from rain and slowly moves through the geological formations of the soil. Ground water is the biggest source of drinking water in India as more than three-quarters of the Indian population depends on it but in more than 10 states, it is contaminated by arsenic.

Figure 1.2 Global scenario of ground water utilization.

Table 1.1 Status of ground water in India (5).

Unfortunately, water that is available as ground water resource is also being contaminated with naturally occurring chemicals besides fluoride, arsenic, lead, salt, aluminum, chromium, copper, pathogens, ammonia, nitrates or nitrites. Permissible and desirable limits of a few essential characteristics that determine the quality of water can be obtained from Table 1.2 [6]. Metal poisoning and bacterial contamination has also affected the ground water apart from contamination by fluoride, arsenic and nitrates. Arsenic levels beyond permissible limits in drinking water is the main cause of arsenic toxicity and skin cancer in Taiwan, China, Chile, Argentina, Mexico, India, Hungary Bangladesh, the United States and Thailand. Eleven countries in the world have more than 50% of their population drinking fluoridated water: Australia (80% population), Brunei (95%), Chile (70%), Guyana (62%), Hong Kong (100%), the Irish Republic (73%), Israel (70%), Malaysia (75%), New Zealand (62%), Singapore (100%), and the United States (64%). The graphical representation of fluoride and arsenic affected areas in India can be observed in Figure 1.3 (a) and (b) respectively (7, 8).

Figure 1.3 Range of (a) fluoride in ground water (mg/L)

Figure 1.3 (b) Range of Arsenic in ground water (µg/L) as reported.

Table 1.2 Drinking water specifications by Ministry of Water Resources, (Amended) (6).