Search

The surge in antibiotic use in various industries has led to increased excretion of antibiotic resistance genes (ARG) to the environment, this poses threat to human and animal health. The dairy industry particularly dairy farms have been identified as one of the large contributors of antibiotic resistant bacteria (ARB) and ARG in the environment. The unregulated use of antibiotics and the use of disinfectants in the clean in place (CIP) process and heavy metal used for animal feed has been said to result in the induction of antibiotic resistance genes in pathogenic bacteria present in dairy wastewater (DWW). Disinfectant and heavy metals induce antibiotic resistance by inducing efflux pump genes which induce co-selection and cross-selection. There are several studies reporting cross and co-selection between heavy metals, disinfectants such as H2O2 and antibiotics which induce ciprofloxacin and ampicillin resistance in Staphylococcus aureus, while Zn resistance genes(czrC) and methicillin resistance gene (mecA) select for Methicillin-resistant Staphylococcus aureus (MRSA). Controlling the spread of antimicrobial resistance in the environment requires a thorough understanding of their causes. Hence, this review aims to provide an overview of the role chemical materials present in DWW such as CIP chemicals, heavy metals in induction of antibiotic resistance through co- and cross-selection. Additionally, and their mechanism of co- and cross-selection resistance, their pathway to the environment and preventative measures are also discussed.

ABSTRACTCement production processes contribute to around 5% of carbon emissions globally and increase yearly. To cut 5% of global emissions, alternative materials to substitute cement concentration in building materials must be sourced. This review identified some agricultural waste, such as sugarcane bagasse ash (SBA), palm leaf ash, and rice husk ash, with potential materials for partial substitution or replacement for cement. It also discusses the influence of incorporating agricultural waste on critical properties of building materials such as bricks, interlocks, concrete, and pavements. Adding these agricultural wastes could increase bricks’ strength by 65% and reduce unit weight by 25%. It also improves bio bricks’ compressive strength, water resistance, and bulk density. Optimising agricultural waste-loading-producing building materials is critical to their performance and must be considered for developing brick materials with improved properties. The review established that 50% of cement concentration could be replaced with SCBA, or hybridising rice husk ash, agricultural olive waste (AOW), sugarcane leaf waste ashes (SLWA), and rice husk (RH). This suggested that 100% of cement is achievable by exploring hybridising SCBA, a combination of rice husk, (AOW), (SLWA), and (RH) to develop a sustainable material without compromising the required properties for construction application. Incorporating agricultural waste is a viable way to develop more cost-effective and sustainable building materials with no cement content, resulting in a 5% global emission cut and a low-carbon environment.

We review the conversion of waste biomass into recyclable materials using different methods of materials treatment such as thermal, mechanical and chemical processes. Renewable and sustainable biomaterials are increasingly becoming alternatives for synthetic strong materials, e.g. composites. The type of treatment of biomaterial will determine the form to which the biomass is converted and its subsequent applications. It is anticipated that the transformation will produce materials that have superior qualities, properties and characteristics. These include biopolymer materials such as cellulose and hemicellulose, which have all been obtained as products of treatment and extraction from plant materials such as lignocellulose. The main reason for inefficient biomass conversion has been found to be poor manipulation of composite properties during biomass treatment process. The treatment processes are expected to facilitate dehydration, dehydrogenation, deoxygenation and decarboxylation of the bulk biomass materials to target the formation of new compounds that may be used to make strong materials. Significance: This work demonstrates that plant material, as a solid-state biomass material for strong structural applications such as in biocomposites, is affected by factors that include the alignment of fibres, orientation of fibres, and mass density distribution. However, biocomposite materials have been found to be non-toxic, corrosionresistant, low-cost, and renewable. They are preferred because the materials possess high thermal stability, are biodegradable and recyclable, and have high biocompatibility, performance, strength, water-resistance, specific surface area and aspect ratio to qualify them for applications including biobricks for construction, slabs for paving, vehicle internal components, ultra-high temperature aerospace ceramics, and energy storage devices.

Biological nutrient removal is an integral part of a wastewater treatment plant. However, the microorganism responsible for nutrient removal is susceptible to inhibition by external toxicants such as heavy metals which have the potential to completely inhibit biological nutrient removal. The inhibition is a result of the interaction between heavy metals with the cell membrane and the deoxyribonucleic acid (DNA) of the cell. Several attempts, such as the addition of pretreatment steps, have been made to prevent heavy metals from entering the biological wastewater systems. However, the unexpected introduction of heavy metals into wastewater treatment plants result in the inhibition of the biological wastewater treatment systems. This necessitates the recovery of the biological process. The biological processes may be recovered naturally. However, the natural recovery takes time; additionally, the biological process may not be fully recovered under natural conditions. Several methods have been explored to catalyze the recovery process of the biological wastewater treatment process. Four methods have been discussed in this paper. These include the application of physical methods, chelating agents, external field energy, and biological accelerants. These methods are compared for their ability to catalase the process, as well as their environmental friendliness. The application of bio-accelerant was shown to be superior to other recovery strategies that were also reviewed in this paper. Furthermore, the application of external field energy has also been shown to accelerate the recovery process. Although EDTA has been gaining popularity as an alternative recovery strategy, chelating agents have been shown to harm the metal acquisition of bacteria, thereby affecting other metabolic processes that require heavy metals in small amounts. It was then concluded that understanding the mechanism of inhibition by specific heavy metals, and understanding the key microorganism in the inhibited process, is key to developing an effective recovery strategy.

Biological treatments are integral processes in wastewater treatment plants (WWTPs). They can be carried out using sludge or biofilm processes. Although the sludge process is effective for biological wastewater systems, it has some drawbacks that make it undesirable. Hence, biofilm processes have gained popularity, since they address the drawbacks of sludge treatments, such as the high rates of sludge production. Although biofilms have been reported to be essential for wastewater, few studies have reviewed the different ways in which the biofilm properties can be explored, especially for the benefit of wastewater treatment. Thus, this review explores the properties of biofilms that can be exploited to enhance biological wastewater systems. In this review, it is revealed that various biofilm properties, such as the extracellular polymeric substances (EPS), quorum sensing (Qs), and acylated homoserine lactones (AHLs), can be enhanced as a sustainable and cost-effective strategy to enhance the biofilm. Moreover, the exploitation of other biofilm properties such as the SOS, which is only reported in the medical field, with no literature reporting it in the context of wastewater treatment, is also recommended to improve the biofilm technology for wastewater treatment processes. Additionally, this review further elaborates on ways that these properties can be exploited to advance biofilm wastewater treatment systems. A special emphasis is placed on exploiting these properties in simultaneous nitrification and denitrification and biological phosphorus removal processes, which have been reported to be the most sensitive processes in biological wastewater treatment.

The kinetics of free cyanide biodegradation were investigated under simulated winter (5 °C) and optimum conditions (22 °C and pH of 11) using a Fusarium oxysporum isolate grown on Beta vulgaris waste as a sole carbon source in the presence of heavy metals, i.e. As, Fe, Cu, Pb, and Zn. The highest free cyanide degradation efficiency was 77% and 51% at 22 °C and 5 °C respectively, in cultures containing free cyanide concentration of 100 mg F-CN/L. When compared with the simulated winter conditions (5 °C), the specific population growth rate increased 4-fold, 5-fold, and 6-fold in 100, 200 and 300 mg F-CN/L, respectively, for cultures incubated at 22 °C in comparison to cultures at 5 °C; an indication that the Fusarium oxysporum cyanide degrading isolate prefers a higher temperature for growth and cyanide biodegradation purposes. The estimated energy of activation for cellular respiration during cyanide degradation was 44.9, 54, and 63.5 kJ/mol for 100, 200, and 300 mg F-CN/L cultures, respectively, for the change in temperature from 5 to 22 °C.

A microorganism isolated and identified as Acinetobacter courvalinii was found to be able to perform sequential free cyanide (CN−) degradation, simultaneous nitrification and aerobic denitrification (SNaD); this ability was associated with the multiphase growth profile of the microorganism when provided with multiple nitrogenous sources. The effect of CN− on SNaD including enzyme expression, activity and protein functionality of Acinetobacter courvalinii was investigated. It was found that CN− concentration of 1.9 to 5.8 mg CN−/L did not affect the growth of Acinetobacter courvalinii. Furthermore, the degradation rates of CN− and ammonium-nitrogen (NH4-N) were found to be 2.2 mg CN−/L/h and 0.40 mg NH4-N/L/h, respectively. Moreover, five models’ (Monod, Moser, Generic Rate law, Haldane, and Andrews) ability to predict SNaD under CN− conditions, indicated that, only the Rate law, Haldane and Andrew’s models, were suited to predict both SNaD and CN− degradation. The effect of CN− on NH4-N, nitrate-nitrogen (NO3−) and nitrite-nitrogen (NO2−) oxidizing enzymes indicated that the CN− did not affect the expression and activity of ammonia monooxygenase (AMO); albeit, reduced the expression and activity of nitrate reductase (NaR) and nitrite reductase (NiR). Nevertheless, a slow decrease in NO2− was observed after the supplementation of CN− to the cultures, thus confirming the activity of NaR and the activation of the denitrification pathway by the CN−. These special characteristics of the Acinetobacter courvalinii isolate, suggests its suitability for the treatment of wastewater containing multiple nitrogenous compounds in which CN− is present.