Air diffusers or spargers have since been used in separation processes that include conventional wastewater treatment. Over the years, there has been advancements in diffuser design in terms of shape, pore size, orientation and materials of construction as a way of mitigating challenges such as fouling, clogging, energy consumption and poor system efficiency. Some of the available air diffusers are inadequate to solve most of these challenges due to reduced quality and increased quantity of wastewater being treated. Additionally, there is a paucity of information regarding air diffuser design and their effect on operational parameters in wastewater treatment. This review seeks to address the advancement in diffuser design and also the effects of design factors including parameters of air diffusers with a focus of their use in a column flotation system for wastewater treatment.

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.

Activated sludge (AS) treatment systems’ major limitation is the nuisance foaming at the surface of the aeration basin in wastewater treatment plants (WWTPs). This foam can be stabilized by biofoamers and surfactants in the wastewater to be treated. In order to control foam, synthetic defoamers are used; however, these defoamers are toxic to the environment. This study aimed to optimize the production of biodefoamers by quantifying foam reduction efficiency and foam collapse by the isolate pervasive to poultry slaughterhouse wastewater (PSW). Before their identification and characterization, nine bacterial isolates were isolated and assessed for foam reduction efficiency. These organisms produced minute biodefoamers under various conditions generated on the response surface methodology (RSM). The isolates that produced biodefoamers with high foam reduction efficiency and at a lower foam collapse rate were Bacillus, Aeromonas, Klebsiella, and Commamonas spp. consortia. At 4% (v defoamer/v PSW), the crude defoamers produced by the consortium had 96% foam reduction efficiency at 1.7 mm/s foam collapse rate, which was comparable to 96% foam reduction efficiency and 2.5 mm/s foam collapse rate for active silicone polymer antifoam A/defoamer by Sigma-Aldrich, a synthetic defoamer. At 2.5 mm/s, all of which were achieved at pH 7 and in less than 50 s. The application of the biodefoamer resulted in sludge compacted flocs, with filament protruding flocs observed when a synthetic defoamer was used. The biodefoamer showed the presence of alkane, amine, carboxyl and hydroxyl groups, which indicated a polysaccharide core structure. The 1H NMR analysis further confirmed that the biodefoamers were carbohydrate polymers. This study reports for the first time on the efficiency and comparability of a biodefoamer to a synthetic defoamer.