**1. Introduction**

The modern-day world has seen a boom in industrial activities. Due to extensive manufacturing activities taking place, large volumes of waste are produced, including wastewaters which are of major interest for re-use due to the scarcity of potable water in most countries. The wastewater produced poses serious environmental problems in its disposal. Because of new products that are emerging and being manufactured, so are new and recalcitrant wastes produced in production lines. Convectional wastewater technologies may be limited to process these contaminants, further exacerbating the problems the world is already facing with respect to potable water. Hence, there is a dire need to develop new methods to mitigate

wastewater's effect on the already degrading environment. On the other hand, clean, fresh potable water has become scarce especially in most African countries due to contamination by intensive industrial activities. To date over one hundred technologies for the treatment of organic and inorganic wastewater streams have been documented; several of these technologies have been emerging and these range from chemical and physical to biological methods. This book chapter focuses on the emerging trends of wastewater treatment technologies, with respect to membrane and biological methods.

Exhibiting high levels of novelty in purification technologies, membranes have been widely used and serve a crucial role in various fields, such as fatty and oily industrial water treatment [1–3].

Microalgae-based technologies are autotrophic in nature and microalgae is a highly potential atmospheric carbon fixation technology. After upstream treatment processes, microalgae technology is usually employed as secondary or tertiary treatment process for effluents that are laden with inorganic components such as nitrogen and phosphorus which cause eutrophication and more long term challenges that are caused by organic material and heavy metals in disposed of wastewater. Microalgal processes then chip in to offer at attractive dimension for the treatment of wastewater coupled with the generation of possibly biomass of high value which can further used for various purposes. Microalgae has minimal risk of production of secondary pollution because of its ability to use inorganic nitrogen and phosphorus for their growth; and their ability to remove heavy metals and toxic organics [4–6].

Another powerful, emerging treatment methodology is the Microbial fuel cells (MFCs) technology which capitalizes on the bioelectrical catalytic activity of microorganisms to generate electric power by oxidizing the organic matter and sometimes inorganic material in wastewater. MFC technology offers a dual goal as it allows for energy recovery and wastewater treatment in a single configuration [7, 8].

#### **2. Wastewater contaminants**

The term wastewater is said to be water containing contaminants mainly due to human use. It emanates from diverse sources such as domestic, commercial, agricultural, or infiltration and storm run-off, with most wastewater being 99.9% water and the rest solids [9]. The characteristics of wastewater are usually determined by the chemical components and flow conditions, as this is used in the design of each wastewater treatment plant [10]. The flow conditions of wastewater are based on the seasons and it is mainly the wet season which will result in an inflow of storm run-offs. The organic and inorganic constituents of wastewater are used as an indicator of the chemical quality of wastewater. The following parameters are usually considered when measuring the chemical characteristics of wastewater; biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids (TS), volatile solids (VS), total nitrogen (TN), total phosphorus (TP), pH and alkalinity [11]; among others.

#### **2.1 Chemical oxygen demand (COD)**

This is usually a representative of the contaminants in wastewater as the higher the COD content in wastewater, the higher the degree of contamination. The COD content in industrial wastewater is usually higher when compared to that of domestic/municipal wastewater as presented in **Table 1**. It gives an indication of the degree of biodegradation in wastewater when compared with BOD as the ratio of BOD to COD higher than 0.5 makes the wastewater biologically treatable [16]. It is

*Emerging Trends in Wastewater Treatment Technologies: The Current Perspective DOI: http://dx.doi.org/10.5772/intechopen.93898*


#### **Table 1.**

*Characteristics of raw industrial wastewater [12–15].*

measured as the quantity of oxygen required to stabilize the carbonaceous organic matter chemically. It is used to quantify the organic matter, nitrite, sulphide and ferrous salts present in wastewater [17].

COD in wastewater could either be readily biodegradable matter, active autotrophic and heterotrophic biomass, soluble inert organic matter, inert inorganic matter [18]. Generally, the COD content in wastewater is either soluble or particulate (suspended). Classification of domestic wastewater based on COD include low (300-500 mg/L), medium (500-750 mg/L) and high (700 – 1200 mg/L) strength wastewater [19]. According to Henze and Comeau [19], the degradable COD content of a typical medium strength is 90% for soluble COD, 66% for particulate COD and 76% for total COD while the remaining percent are the inert component. The use of membrane technology only is very effective for low-strength wastewater [20] but the efficiency can be increased when combined with other technologies for treatment of high strength wastewater such as seen in the study by Matheus et al. [21] where microfiltration and nanofiltration was preceded by coagulation and flocculation to achieve a 96% COD removal (from 4610 mg/L to 184 mg/L) for dairy wastewater. Wastewater with high COD content usually causes fouling for the membrane [21], therefore, the use of biological treatment techniques such as microalgae and microbial fuel cell are more appropriate for high strength wastewater [22, 23].

#### **2.2 Biochemical oxygen demand (BOD)**

This is the quantity of oxygen required by microorganisms for the decomposition of organic matter under aerobic conditions. As stated for COD, BOD is also an indication of the degree of contamination, it affects the amount of dissolved oxygen required by aquatic organisms, and if lower than 6 mg/L could lead to their death. The typical BOD value of domestic wastewater with minor industrial wastewater in it ranges from 100 – 200 mg/L, 200 – 300 mg/L and 300 – 560 mg/L for low, medium and high strength wastewater [19]. The relationship between BOD and dissolved oxygen is inversely proportional, as a low dissolved oxygen indicates a high BOD content in wastewater [24]. However, as the organic biodegradable content of water increases, the BOD increases also [25]. Since increase in biodegradable organic pollutants is an increase in the BOD, therefore, most biological treatment processes such as microalgae or microbial fuel cell technique can remove the BOD content in wastewater. Zhang et al. [26], indicated a 98.6% BOD removal using MFC while Marassi et al. [27] reported a 96-97% efficiency using a tubular MFC. The use of microalgae has also been reported to have effectively reduce the BOD content of wastewater by generation of O2 during photosynthesis [28] and 87% removal efficiency [29].

#### **2.3 Total solid (TS)**

This is the organic and inorganic matter; suspended and dissolved solids; settleable and volatile solid content of wastewater. Though physical separation techniques easily remove most suspended solids, some still find their way into the environment. The dissolved and volatile solid (VS) contents are a representative of the degradable content in wastewater; therefore, some treatment techniques do account for the number of volatile solids removed. The VS content of wastewater, likewise, indicate its strength as higher VS indicate high strength wastewater and vice versa. The more the VS content of wastewater, the greater the impact on the treatment plant as it is an indication of the organic solid content. Total dissolved solids (TDS) are composed of inorganic salts and small quantities of organic matter dissolved in water. TDS in wastewater increases due to chemicals either from washing, cleaning, and production processes [30].

#### **2.4 Total nitrogen and phosphorus**

These are plant nutrients that are present in wastewater as either nitrates or ammonia, and fertilizer manufacturing companies usually generate them, agricultural sectors and industries that utilize corrosion inhibitors. Total nitrogen is the combination of both the inorganic and organic nitrogen, and ammonia in wastewater, it exists as either nitrate, nitrite, ammonium, and organic dissolved compounds such amino acids, urea, and organic nitrogen composites. In aquatic ecosystems, phosphorus is also present as phosphates such as orthophosphates, condensed phosphates and phosphates organically bound [25].

Nitrogen and phosphorus in wastewater cause eutrophication in water bodies which can lead to the death of aquatic habitats, if discharged without treatment [31]. High removal rate of nitrogen and phosphorus have been achieved using microalgae treatment process with industrial application of this technique been reported to achieve between 87 and 93% removal [32].

#### **2.5 Metals**

Metals are generally found in wastewater, mainly from the manufacturing, mining, and textile industries. Metals such as arsenic, iron, chromium, lead, copper, tin, sodium, potassium, mercury, aluminum, and nickel are common pollutants in industrial wastewaters [33]. Industries such as iron and steel, mining, micro-electronics, and textiles often generate wastewater with heavy metals therein. Metals in wastewater lead to an increase in the treatment costs, and they are known to cause varying environmental problems such as distortion in plant growth, algal bloom, death of aquatic biota, debris formation and sedimentation [34]. Human related health effects include carcinogenicity, chronic asthma, skin related problems, depression, internal organ damage, coughing and nervous system-related diseases [35].

The presence of metal in wastewater in low concentration (1-3 mg/L) is toxic because metals are non-biodegradable and some metals do accumulate overtime [33, 36]. Although some metals which are essential to human, animal and plants may still be tolerated in minimal quantities such as copper, zinc, chromium but above the limit required can be toxic. An example is the reproduction of water flea Daphnia affected by exposure to 0.01 mg hexavalent chromium/L, therefore, the lethal chromium level for several aquatic and terrestrial invertebrates has been reported to be 0.05 mg/L. Some elements, however, such as arsenic, lead, cadmium, mercury is known to be toxic to living beings at any concentration and are not required to be taken into the body even at ultra-trace level [33].
