A Review of Current Achievements and Recent Challenges in Bacterial Medium-Chain-Length Polyhydroxyalkanoates: Production and Potential Applications.

Using petroleum-derived plastics has contributed significantly to environmental issues, such as greenhouse gas emissions and the accumulation of plastic waste in ecosystems. Researchers have focused on developing ecofriendly polymers as alternatives to traditional plastics to address these concerns. This review provides a comprehensive overview of medium-chain-length polyhydroxyalkanoates (mcl-PHAs), biodegradable biopolymers produced by microorganisms that show promise in replacing conventional plastics. The review discusses the classification, properties, and potential substrates of less studied mcl-PHAs, highlighting their greater ductility and flexibility compared to poly(3-hydroxybutyrate), a well-known but brittle PHA. The authors summarize existing research to emphasize the potential applications of mcl-PHAs in biomedicine, packaging, biocomposites, water treatment, and energy. Future research should focus on improving production techniques, ensuring economic viability, and addressing challenges associated with industrial implementation. Investigating the biodegradability, stability, mechanical properties, durability, and cost-effectiveness of mcl-PHA-based products compared to petroleum-based counterparts is crucial. The future of mcl-PHAs looks promising, with continued research expected to optimize production techniques, enhance material properties, and expand applications. Interdisciplinary collaborations among microbiologists, engineers, chemists, and materials scientists will drive progress in this field. In conclusion, this review serves as a valuable resource to understand mcl-PHAs as sustainable alternatives to conventional plastics. However, further research is needed to optimize production methods, evaluate long-term ecological impacts, and assess the feasibility and viability in various industries.

Removal of most frequent microplastic types and sizes in secondary effluent using Al2(SO4)3: choosing variables by a fuzzy Delphi method.

Microplastics (MPs) as an emerging pollutant can affect aquatic organisms through physical ingestion, chemical problems and possible creation of biological layers on their surfaces in the environment. One of the significant ways for MPs to enter the aquatic environment is through the effluent discharge of wastewater treatment plants (WWTPs). In this study, first, the concentration and characteristics of MPs in secondary wastewater effluent, and the influential variables related to the coagulation process, for MPs removal were identified using systematic reviews of previous studies. Then, the most proper MPs characterization and coagulation variables were chosen by experts' opinions using a fuzzy Delphi method. Therefore, the experiment tested in conditions close to the full-scale wastewater treatments. Finally, in the laboratory removal of MPs by coagulation of polyamide (PA), polystyrene (PS), and polyethylene (PE), < 125 and 300-600 µm in size, was tested by a jar test applying Al2(SO4)3 in doses of 5 to 100 mg/L plus 15 mg/L polyacrylamide as a coagulant aid. Using R and Excel software, the results were analyzed statistically. It was concluded that the maximum and minimum removal efficiency was 74.7 and 1.39% for small PA and large PE, respectively. Smaller MPs were found to have higher removal efficiency. The MPs type PA achieved greater removal efficiency than PS, while PE had the least removal efficiency.

Microplastics removal from aquatic environment by coagulation: Selecting the best coagulant based on variables determined from a systematic review.

The present study was carried out in the two phases of systematic review and experimental research. First, for the systematic review phase, Web of Science, Scopus, and PubMed as electronic databases were utilized to find research articles distributed up to March 5, 2021, related to the removal of microplastics by coagulation. In total, 104 publications were found, of which 14 were reviewed for deriving the variables and research design. Then, in the experimental phase, the experiment was carried out based on the variables derived from the systematic phase for three microplastic types (polyethylene, polystyrene, and polyamide) and five coagulants (polyaluminum chloride (PAC), ferric chloride (FeCl3), aluminum chloride (AlCl3), alum (Al(OH)3) and aluminum sulfate (Al2(SO4)3)) in bench scale study. The differences between removal efficiencies in terms of type, shape, concentration, and size of microplastics within the looked into article was analyzed utilizing ANOVA or Kruskal-Wallis test (for parametric or nonparametric analysis, respectively). The results of experimental phase show that the removal efficiency of different microplastics was significantly different, and it was equal to 65, 22, and 12% on average for PA, PS, and PE, respectively. These averages are much lower than the average removal efficiency calculated in the reviewed articles (78 and 52% for PS and PE, respectively). The removal efficiency of microplastics types by coagulants was not significantly different. As a result, a coagulant that has the lowest dose can be selected as the most suitable coagulant, which is Al(OH)3 in this study.

Tracking microplastics contamination in drinking water in Zahedan, Iran: From source to consumption taps.

Microplastics (MPs) that pollute drinking water are inherently toxic, act as an adsorbent of hazardous pollutants, and threaten human health. So, the fate of microplastics in drinking water from the source to consumption taps (CTs) was assessed in spring and winter in Zahedan city in Iran. Sampling was performed from 4 reservoirs (raw water), before and after two water treatment plants (WTPs), and 10 CTs. The reservoirs were sampled using a plankton net (pore size = 100 µm), and the remaining samples were taken using a sampling device (containing a stainless steel membrane as a filter with pore size = 5 µm). The combination of density separation techniques, digestion, observation, Micro-Raman and FTIR, and SEM analysis was performed to recognize MPs. The average number of MPs in raw water varied between 15.4 and 44.7 MP/m3 (winter) and 22-51.8 MP/m3 (spring). The results before and after the treatment plant showed that about 64 % and 75 % of particles were eliminated in WTP1 and WTP2, respectively. The average number of MPs in CTs was more than treatment water (CTa = 85-390 MP/m3 and CTb = 75-400 MP/m3), which is a probable confirmation of secondary contamination (abrasion from pipes, installations, and sealing materials). The dominant type of polymer detected in raw water, treated water, and consumption taps were PS. The estimated daily intake for children and adults was about 0.16-15 MP/kg/bw/year and 0.07-5.7 MP/kg/bw/year, respectively. The surface morphology of MPs showed that the particles were affected by continuous weathering, mechanical breakage, and oxidation. MPs threaten the environment and human health due to the adsorption and transport of hazardous pollution and their intrinsic toxicity, so a solution must be thought of to prevent the pollution of drinking water by MPs.

The effect of size distribution of ambient air particulate matter on oxidative potential by acellular method Dithiothreitol; a systematic review.

Today air pollution caused by particulate matter (PM) is a global issue, especially in densely populated and high-traffic cities. The formation of reactive oxygen species (ROS) by various toxicological studies is considered as one of the important effects caused by airborne particles that can lead to adverse effects on human health. In this study, to answer the question of whether particle size affects oxidative potential (OP), we searched the main databases, including PubMed, Scopus, Embase, and Web of Science, and defined search strategy based on the MESH terms for the above-mentioned search engines. All articles published until 2021 were searched. An ANOVA was run using R software to show the correlation between the size distributions of particulate matter and oxidative potential (base on mass and volumetric units) in ambient air. As expected, the regression results showed that the relationship between particle size and OP values for the studies based on mass-logarithm has a significant difference in the different distribution size categories, which was related to the difference between the <2.5 and < 1 categories. However, ANOVA analysis did not show a significant difference in the volumetric OP logarithm in the different distribution size categories. In this study, it was found that sizes higher than 2.5 µm did not have much effect on human health, and it is recommended that future research focus on PM2.5. Supplementary Information: The online version contains supplementary material available at 10.1007/s40201-021-00768-w.

Evaluation of conventional wastewater treatment plants efficiency to remove microplastics in terms of abundance, size, shape, and type: A systematic review and Meta-analysis.

In the present study Web of Science, Scopus, and PubMed as electronic databases were used to find work published up to October 27, 2020 about microplastics evaluation in conventional wastewater treatment plants. In total, 407 publications were found, of which 77 were eligible for meta-analysis. A comprehensive meta-analysis was undertaken to evaluate the relevant publications regarding microplastics abundance. The average microplastics abundance was within the 1-31,400, 0.2-12,580, 0.002-7863, and 0.003-447 items range per liter wastewater for influent, primary, secondary, and tertiary treatment steps, respectively. The difference between the abundance of microplastics characterization for the different treatment steps was analyzed using ANOVA or Kruskal-Wallis test (depending on the data distribution). According to the pooled data, the average microplastics abundance was 124.04, 20.67, 5.62, and 1.97 (items/l) for influent, primary, secondary, and tertiary treatment. The results of Egger's test (t = 7.49, P ≤ 0.0001) were statistically significant, suggesting the existence of publication bias.

Blood lead level monitoring related to environmental exposure in the general Iranian population: a systematic review and meta-analysis.

Exposure to lead can cause adverse health problems incorporating hypophosphatemia, heart and liver disease, cancers, neurological and cardiovascular diseases, central nervous disorders, and sensory disorders. This study investigated the blood lead level in the general Iranian population with environmental exposure to lead. In the presented systematic review and meta-analysis, the authors searched Iranian dataset, including Magiran, SID, Iranmedex, and Nopa, and the main dataset, comprising PubMed, Scopus, Embase, and Web of Science, all available articles until 12 January 2019, and extracting 55 studies (with 63 data for analysis) to a meta-analysis. A comprehensive meta-analysis software, pooled standard deviation, mean, sample size, and the utterly random effects model was analyzed in this study. The results showed that the overall mean BLL (95% CI) in total inquiries was 6.41 µg/dL (5.96 to 6.87). Besides, the results for gender and age subgroups were as follows: mean BLL, 6.47 µg/dL, 95% CI, 5.79, to 7.15, mean BLL, 6.44 µg/dL, 95% CI, 5.96, to 6.91, respectively. Conclusively the mean BLL in the Iranian population was higher than the recommended level by the US Centers for Disease Control and Prevention (CDC). Results indicated that the mean BLL in men and adults was more elevated than in women and children, respectively. Therefore, BLL monitoring and screening of the general Iranian population are is necessary to determine a reference value.

Zeolite-intermittent cycle moving bed air-lift bioreactor (Zeo-ICMBABR) for composting leachate treatment; simultaneous COD, nitrogen and phosphorous compounds removal.

Anaerobically pretreated composting leachate contains high ammonia load and soluble organic matter, which requires further treatment. In this study, simultaneous removal of COD, nitrogen, and phosphorus compounds from anaerobically pretreated composting leachate investigated by using an intermittent cycle moving bed airlift bioreactor (ICMBABR) supported by zeolite as a biofilm. The efficiency of COD, Total Kjeldahl Nitrogen (TKN), and phosphorous removal and contaminants profile during the process, and the mass balances were analyzed. A multilayer design used for the experimental design, and the effect of four variables including hydraulic retention times (4, 6, 8 h), the zeolite ratios (20, 35, 50%), the influent COD concentration (1, 2, and 3 g/L) and aeration duration (64, 73, and 82%) investigated by Response Surface Methodology (RSM). According to the results and process profile the sequence of anoxic and aerobic conditions, presence of the anaerobic zone in the bottom of the reactor, as well as the use of zeolite as adsorbent media, significantly allowed the simultaneous removal of COD (99%), TKN (95%), and total phosphorus compounds (90%) from anaerobically pretreated composting leachate and favorable potential to remove nitrogen compounds by high efficiency (79%) through simultaneous nitrification and denitrification (SND).

Synthesized Cr/TiO2 immobilized on pumice powder for photochemical degradation of acid orange-7 dye under UV/visible light: influential operating factors, optimization, and modeling.

The current study aimed to investigate the removal efficiency of acid orange-7 (AO7) using synthesized Cr/TiO2 immobilized on pumice powder under visible light and UV irradiation. The characterization of synthesized nanocatalyst examined by scanning electron microscope, X-ray diffraction, and Fourier transforms infrared. The optimum of experimental parameters including catalyst dosage, dye concentration, time and pH, D-optimal Design (DOD) along with response surface methodology obtained by R software. The initial and outlet concentration was measured using a spectrophotometer. Besides, Analysis of variance results for the quadratic model showed simple linear regression with high significance and provided as a predicting model. The differences less than 0.2 between multiple and adjusted R2 in two models indicate that two examined models fitted suitably. The highest removal efficiency of AO7 was 95 and 74% under visible and UV irradiation, respectively. Therefore, the higher removal efficiency in visible light reduces the costs and energy, moreover, offers an environmentally friendly method. The results showed that the removal efficiency of AO7 increased considerably with rising catalyst dosage and time, as well as minimizing dye concentration, and pH.

Data for efficiency comparison of raw pumice and manganese-modified pumice for removal phenol from aqueous environments-Application of response surface methodology.

Present deadest collection was aimed to evaluate the efficiency of raw pumice (RWP) and Mn-modified pumice (MMP). Response surface methodology (RSM) based on the central composite designs (CCD) was applied to evaluate the effects of independent variables including pH, adsorbents dosage, contact time and adsorbate concentration on the response function and the best response values were predicted. The Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the adsorbents. Based on acquired data, the maximum efficiency removal of phenol was obtained 89.14% and 100% for raw and Mn-modified pumice respectively. The obtained data showed pH was effective parameter on phenol removal among the different variables. Evaluation of data using isotherms and kinetics models showed the fitted with Langmuir isotherm and pseudo second order kinetic for both adsorbents. According to obtained data was observed that modification of pumice can improve the efficiency removal of phenol to meet the effluent standards.

Acid pretreatment and enzymatic saccharification of brown seaweed for polyhydroxybutyrate (PHB) production using Cupriavidus necator.

The brown seaweed Sargassum sp. was used as a feedstock to produce polyhydroxybutyarte (PHB) using Cupriavidus necator PTCC 1615. In order to release monomeric sugars, dilute acid hydrolysis of Sargassum sp. biomass was followed by enzymatic saccharification. In addition, the effect of different nitrogen sources was evaluated for PHB production. The fermentation of hydrolysate with the ammonium sulfate as selected nitrogen source resulted PHB yield of 0.54±0.01g/g reducing sugar. Then, NaCl was used as external stress factor which was added to the media. Addition of 8g/L NaCl had a positive impact on high PHB yield of 0.74±0.01g/g reducing sugar. Increasing trend of NaCl concentration to 16g/L was found to inhibit the production of PHB. Based on obtained results using 20g/L of reducing sugar, at desired condition the highest cell dry weight and PHB concentrations were 5.36±0.22 and 3.93±0.24g/L, respectively. The findings of this study reveal that Sargassum sp. is a promising feedstock for biopolymer production. The characteristics of produced PHB were analyzed by FTIR, differential scanning calorimetry and 1H NMR.