Abstract
Conventional wastewater treatment consists of chemical, biological, physicochemical, and mechanical processes to remove organic loading, solids, and nutrient contents from wastewater. Biological processes are more commonly used in wastewater treatment as secondary or tertiary treatments, as it is more effective and more economical than chemical and mechanical processes. In this chapter, several types of wastewaters generated from municipal or industrial activities are discussed. Wastewater has different pollutant contents depending on the point of generation which consequently requires different ways of treatment. Some commonly used conventional wastewater treatment technologies are introduced. A particular focus is given to both aerobic and anaerobic treatments.
TopIntroduction
Wastewater is any water which has been adversely affected in quality by anthropogenic influences. The wastewaters are originated from human wastes, cesspit leakage, septic tank discharge, sewage treatment plant leakage, washing water, surface water contaminated by sewage, groundwater infiltrated into sewage and industrial wastes. In general, the wastewaters can be categorised into domestic or sanitary wastewater, wastewaters from institutions, industrial wastewater, infiltration into sewers, stormwater, leachate and septic tank wastewater. The composition of wastewater changes widely. The wastewater may contain about 90% of water, microorganisms, organic materials, nutrients, metals, odour and taste and radioactivity. The characteristics of wastewaters may vary according to their point sources.
Wastewater needs to be treated as they pose harmful hazards to human and the environment. Several major sources of wastewater in Sabah will be discussed, which includes sewage and palm oil mill industry wastewater which are discussed in Chapter 10 and Chapter 11 respectively, and oil and gas industry wastewater, urban wastewater, nonpoint source, wastewater from floating residential areas, and other industrial wastewaters which are discussed in the subsequent sections. A particular focus is given to the wastewater characteristics and status of its treatment and management.
The most common wastewater treatment methods are using conventional wastewater treatments. Conventional wastewater treatments plants generally combine the chemical processes, physicochemical processes, biological processes, and mechanical processes. In this chapter, the discussion is centralized to the biological treatment processes as the chemical and physicochemical processes are already discussed in Chapter 6. Some of these processes can be used interchangeably between water and wastewater treatment.
Biological wastewater treatment is a critical part of any wastewater treatment plants for treating both municipal and industrial wastewaters. Biological processes possess economic value in both capital and operating expenses as compared to some other chemical processes (Mittal, 2011). Biological treatments can be operated under anaerobic or anaerobic condition. Aerobic refers to a condition where the microbial reactions occur in the presence of free oxygen, while anaerobic denote a biological reaction that takes place in the absence of free oxygen. These reactions treat the wastes present and produce by-products such as biogas, water, heat, and compost. These conditions are determined depending on the microorganisms involved, i.e. aerobes or anaerobes. Table 1 shows some differences between aerobic and aerobic treatment.
The biological wastewater treatment is discussed in terms of the technologies commonly used to treat various types of wastewater. This includes open ponding, activated sludge, sequencing batch reactor, oxidation ditch, extended aerator, anaerobic digester, trickling filter, rotating biological contactor, septic tank, and Imhoff tank.
Table 1. Differences between aerobic and anaerobic treatments
| Parameter | Aerobic Treatment | Anaerobic Treatment |
| Principle of operation | Microbial reactions take place in the presence of free oxygen | Microbial reactions take place in the absence of free oxygen |
| Reaction rates | Relatively rapid and fast | Relatively time consuming and slow |
| Suitability | Wastewater with low organic concentration | Wastewater with medium and high organic concentrations |
| By-products | Carbon dioxide, water, excess biomass | Carbon dioxide, methane, excess biomass |
| Biomass yield | Relatively high | Relatively low |
| Specific substrate utilization rate | Relatively low | Relatively high |
| Post-treatment | Typically followed by filtration, disinfection, or direct discharge | Typically followed by aerobic treatment |
| Footprint | Relatively large | Relatively small |
| Capital and operating expenses | Relatively high | Relatively low |
| Example of technologies | Activated sludge process, sequencing batch reactor, oxidation ditch, aerobic pond | Anaerobic digester, up-flow anaerobic sludge blanket reactor, anaerobic pond |
Key Terms in this Chapter
Microbes: Microscopic-size organisms found in water, air, and soil which are responsible for many natural processes on earth such as decomposing organic matter and nutrients which is particularly significant in wastewater treatment.
Urban Wastewater: Consists of sewerage produced by residential areas and wastewaters generated from public facilities such as schools, local business, offices and shops lots.
Ponding System: Oxidative treatment of wastewater which is classified into aerobic ponds, anaerobic ponds, facultative ponds, maturation ponds and aerated lagoons.
Activated Sludge Process: Biological process which utilizes aerobic microbes to feed on organic contaminants in wastewater to produce a high-quality effluent.
Wastewater: Any water which has been adversely affected in quality by anthropogenic influences.
Biological Wastewater Treatment: Process that uses natural processes to treat wastewater which involves the microbial activity of decomposing organic and other substances.
Oil and Gas Wastewater: Wastewater that is originated from the oil and gas sector, including flow back and produced water containing toxic chemicals, and other contaminants like heavy metals, hydrocarbons, and salts.
Palm Oil: A vegetable oil extracted from the mesocarp of the oil palm fruits.
Nonpoint Source Pollution: Pollution resulting from a number of human activities such as land development that require land clearing, and will lead to soil erosion carrying the human-made pollutants into water bodies.