Optimization of Polystyrene Biodegradation by Bacillus cereus and Pseudomonas alcaligenes Using Full Factorial Design

Abstract

Microplastics (MP) are a global environmental problem because they persist in the environment for long periods of time and negatively impact aquatic organisms. Possible solutions for removing MP from the environment include biological processes such as bioremediation, which uses microorganisms to remove contaminants. This study investigated the biodegradation of polystyrene (PS) by two bacteria, Bacillus cereus and Pseudomonas alcaligenes, isolated from environmental samples in which MPs particles were present. First, determining significant factors affecting the biodegradation of MP-PS was conducted using the Taguchi design. Then, according to preliminary experiments, the optimal conditions for biodegradation were determined by a full factorial design (main experiments). The RSM methodology was applied, and statistical analysis of the obtained models was performed to analyze the influence of the studied factors. The most important factors for MP-PS biodegradation by Bacillus cereus were agitation speed, concentration, and size of PS, while agitation speed, size of PS, and optical density influenced the process by Pseudomonas alcaligenes. However, the optimal conditions for biodegradation of MP-PS by Bacillus cereus were achieved at γMP = 66.20, MP size = 413.29, and agitation speed = 100.45. The best conditions for MP-PS biodegradation by Pseudomonas alcaligenes were 161.08, 334.73, and 0.35, as agitation speed, MP size, and OD, respectively. In order to get a better insight into the process, the following analyzes were carried out. Changes in CFU, TOC, and TIC concentrations were observed during the biodegradation process. The increase in TOC values was explained by the detection of released additives from PS particles by LC-MS analysis. At the end of the process, the toxicity of the filtrate was determined, and the surface area of the particles was characterized by FTIR-ATR spectroscopy. Ecotoxicity results showed that the filtrate was toxic, indicating the presence of decomposition by-products. In both FTIR spectra, a characteristic weak peak at 1715 cm−1 was detected, indicating the formation of carbonyl groups (−C=O), confirming that a biodegradation process had taken place.

Biodegradation of Typical Plastics: From Microbial Diversity to Metabolic Mechanisms

“…P. aeruginosa isolated from sewage water-contaminated surface soil incubated in nutrient broth (NB) medium for one month PP showed a weight loss of 5.37% [ 48 ]. Moreover, other species of the Pseudomonas , such as Pseudomonas citronellolis [ 49 ], Pseudomonas putida [ 50 ], Pseudomonas alcaligenes [ 51 ], and Pseudomonas fluorescens [ 52 ], have also been shown to degrade different types of plastics.…”

Evaluation of Fenton, Photo-Fenton and Fenton-like Processes in Degradation of PE, PP, and PVC Microplastics

“…The RSM approach involves a series of mathematical techniques aimed at building an empirical model that describes the relationship between the input variables (i.e., the independent variables) and one or more dependent variables (i.e., the response) [52]. Based on our experience in the field of optimization of pollutant degradation in the aquatic environment [53,54], we have assumed that a quadratic model represented by Equation (11) should be sufficient to describe the system with three independent variables and one dependent variable.…”

“…The model coefficients are denoted by a, while x 1 to x 3 represent the values of the three process parameters tested: pH, mass ratio of MPs to iron, and mass ratio of H 2 O 2 to iron. In addition to the linear (x 1 , x 2 , x 3 ) and quadratic (x 1 2 , x 2 2 , x 3 2 ) contributions, the model also includes the interaction terms (x 1 x 2 , x 1 x 3 , x 2 x 3 ) to cover the possible combined effects of the parameters tested, which, as we knew from experience [53][54][55][56][57], are not uncommon in such systems. The area of a broad FTIR band that occurred in the spectral range 3000-3600 cm −1 was used as the response, i.e., as the dependent variable y.…”

Characterization of polystyrene-degrading bacteria isolated from plastic processing plants

“…However, the detailed biodegradation e ciency of PS cannot be compared in all cases, as the PS materials used had different structures (Kim et al 2021) and originated from different sources. In addition, the degradation rate also depends on the presence of nutrients in the medium, temperature, pH, and incubation time, as well as agitation speed, concentration, and size of the PS particles (Miloloža et al 2022). The aforementioned studies directly attempted to investigate the biodegradation of PS in environmental samples such as soils, mangroves, seawater, land ll sediment, activated sludge, waste disposal, and compost previously exposed to abiotic and biotic factors.…”