**2.3 POC in wastewater treatment**

Domestic and industrial activities discharge wastewater containing high concentrations of various contaminants into water bodies [50]. Wastewater usually full of contaminants is considered as any water that is not safe for the intended use. Wastewater as a hazardous substance/material is a by-product resulting from human activities [51]. However, it is a source of chemical and thermal energy. Industrial operations in different mining fields, battery manufacturing, tannery, smelting, electroplating, textile, leather, petroleum processes, etc. are described as the major sources of wastewater. Surface runoff, sewer infiltration and poor management of urban solid waste also generate wastewater. Discharging all these without treatment into watercourses exhausts the good quality of freshwater water bodies. Wastewater is known to contain toxic pollutants like heavy metals, organic substances (dyes, PAHs etc.) posing a great environmental threat for all living organisms [52, 53]. Therefore, reduction in effluent quantity and improving the quality would have major positive effects on land use and human health [51]. To achieve that, compliance with acceptable limits is required prior to discharging effluents into the environment. Researchers have engaged in developing safe, functional, cost-effective, and appropriate wastewater treatment technologies to improve the ecosystem, lessen pollutants' detrimental effects, and minimize the risk of global warming and climate change. Unfortunately, some technologies and materials have shortcomings. As a result, it is imperative to develop safe, cost-effective, and long-lasting wastewater treatment materials.

POC as a waste material have recently been utilized by several researchers for wastewater treatment using techniques such adsorption, biological system etc. Arsenic adsorption with palm oil clinker sand (POCS) was studied by [54]. They found out that pH, arsenic concentration, POCS (mg), and temperature are the four significant variables that control arsenic adsorption. Similar to several other adsorbents, solution initial pH portrays the most prominent influence on adsorption. Water absorption, fitness modulus and specific gravity were said to be the POC properties responsible for arsenic adsorption and process stability. Furthermore, the rich microporous structure and surface functional groups POCs play vital role in the marvelous arsenic adsorption.

In a conventional activated sludge system, POC acted as a submerged attached growth media for the treatment of domestic wastewater. Performance efficiency of the POC in the extended aeration system (EAS) was evaluated by COD, TSS, MLSS, and MLVSS. Comparing the performance of POC submerged system to a biological activated sludge system, it could be concluded that using POC as an attach growth system can reduce the organic contaminant in effluent discharge [55].

POC as a filter media in a sequence batch reactor system is capable of extending its useful life, and reduce the demand for manufacturing new and sustainable media. In a comparative analysis between two SBR reactors with and without POC as a submerged fixed media, the former has higher ammonia removal efficiency of about 90% while the latter has 85% [56]. In a related study treating domestic wastewater in an SBR system, the average removal rate for ammonia and COD were 0.001 mg ammonia/mg MLVSS and 0.0069 mg COD/mg MLVSS respectively. This amount to ammonia and 90% and 70% removal efficiencies for ammonia and COD respectively [57].

#### **2.4 Soil stabilization**

Deep foundations specifically for soft soil has been a problem for long time. This pushed geotechnical engineers to opt for Lightweight Concrete Pile (LCP) due to their peculiar properties such low density, surface roughness, low strength and high porosity. Different materials have been utilized to improve the concrete pile properties for performance enhancement. POC incorporated concrete pile (p-LCP), foamed concrete pile (f-LCP) and normal concrete pile (NCP) for floating foundation were investigated by conducting static and dynamic load tests. Findings revealed that, higher compressive stress and driving resistance values were obtained for p-LCP and f-LCP when compared with NCP. Correlating the compressive stress and driving resistance values of p-LCP and f-LCP with the pile ultimate load carrying capacity, the applied load for p-LCP and f-LCP can be increased by 4.5% and 27.3% respectively. The driving resistance could also be increased by 27.6% and 16.5% for p-LCP and f-LCP, respectively. Therefore, the study concluded that, p-LCP or f-LCP are better than NCP for deep foundation of particular structure in soft soil [58].

#### **2.5 Highway construction**

In the underdeveloped, developing and developed nations, highway construction is vital for the well-being of citizens. This result to the over utilization of natural resources for the construction. However, most of these resources have different environment and financial implications to the immediate community. Therefore, few researchers come up with the idea of using POC waste material for highway pavement construction application and help solve POC disposal issues.

#### *Palm Oil Clinker as a Waste by-Product: Utilization and Circular Economy Potential DOI: http://dx.doi.org/10.5772/intechopen.97312*

A study assessed the effect of using palm oil clinker (POC) as a substitute to fine aggregate on the mechanical properties of stone mastic asphalt (SMA) mixtures. The results proved the suitability of 100% POC replacement for fine aggregate in SMA mixture, as it enhanced the drain down, resistance to moisture damage, resistance to rutting, and resilient modulus when compared to that of control mixture. However, 40% and 60% replacement are considered as the optimum because of their outstanding mechanical properties. It also possesses higher indirect tensile strength for wet and dry conditions. Cantabro loss (durability performance) for POC- 80 and POC-100 exceeded that of the control sample as all mixtures fulfilled the standard requirement of the maximum value (20%) for weight loss. Authors concluded that, the use of POC as fine aggregates can greatly improve asphalt mix performance in flexible pavement construction [19]. In a related study by same authors, using the Marshall mix design, to select the optimum binder content, asphalt mixture samples with different percentages of asphalt binder content (5.0%, 5.5%, 6.0%, 6.5%, and 7.0%) were prepared. The results showed that POC could satisfy the mix design requirements in terms of Marshall stability, flow, quotient, and volumetric properties. However, POC has less effect on optimum binder content. The length of the elastic stage POC replaced mixture is higher than that of the control mixture, thereby, enhancing the elastic properties and making them more inclined towards plastic fracture. The fracture life of asphalt mixtures increases by increasing the POC content in the mix. As a result, the asphalt mixtures are strong and stiff enough to withstand permanent deformation following traffic loads [59].

A study undertaken by [21] employed a high shear mixer to determine the appropriateness of utilizing palm oil clinker fine (POCF) as bitumen modifiers by material characterization tests. The impact of modification mixing parameters was also evaluated. The result from characterization confirmed its pozzolanic property. Thus, suggesting the feasibility of utilizing it as a bitumen modifier. The optimum mixing parameters obtained were 900 rpm at 160°C for 30 min with 6.3% of POCF as the optimum dosage. The study gathered that the incorporation of POCF enhances conventional bitumen properties.

### **2.6 POC as a catalyst**

In the downstream petrochemical industries, ethylene (C2H4) is one of the most highly sought raw materials. C2H4 is a primary precursor for surfactant fabrication, plastic manufacturing and polyethylene production. Rather than landfilling POC, the current work attempted the valorization of silica-rich POC into POC derived SBA- 15 (POC-SBA-15) catalysts and modulation of its surface acidity for C2H4 production via ethanol dehydration. 400oC temperature, 50 wt% ethanol concentration, 16 mL/g.h LHSV were found to be the optimal conditions for ethanol dehydration over POC-SBA-15 [5] with the lowest strong and highest weak acidity. The POC mix catalyzes the process for up to 105 h [26].

#### **2.7 POC as a bio-filler**

To improve the mechanical strength, water resistance and fire protection performance of steel structures, it is essential to use appropriate and cost-effective materials as bio-fillers in solvent-borne intumescent coatings. To that effect, waste by-products like chicken eggshells (CES), rice husk and POC are being used to lessen the use of synthetic fillers. To produce intumescent coatings, POC and hybrid fillers are homogeneously mixed with an acrylic binder and subsequently blended with flame-retardant additives. POC have the advantages of large volume availability and direct usage without further processing.

Study by [3] revealed that, the optimum composition of POC and hybrid fillers results in intumescent coating with the greatest fire retardancy with the lowest equilibrium temperature (171.3°C) because of its high thermal stability, high water resistance and excellent adhesion strength/mechanical properties. POC as a fireretardant filler let the binder to mix appropriately, resulting in a more homogeneous coating with better interfacial bonding. It was discovered that combining POC with Mg(OH)2 fillers also enhances the adhesion strength of intumescent coating.

In a related study by same authors, hybrid fillers with POC were mixed in appropriate quantity of additives and acrylic binder to produce intumescent coatings. Findings revealed that, specimen with POC as a sole filler greatly enhanced the fire protection efficiency of the intumescent coating, with <10% temperature difference when compared to specimen with hybrid fillers. For hybrid fillers composition, specimen consisting of POC/Al(OH)3/TiO2 greatly improved the coatings water resistance due to Al(OH)3 low solubility in water, while specimen containing Mg(OH)2 had higher mechanical strength because of the strong bond that exist between the acrylic binder/Mg(OH)2 filler and metal surface [60].
