Biodegradability of bioplastics in different aquatic environments: A systematic review.

Bioplastics were first introduced as environmentally friendly materials, with properties similar to those of conventional plastics. A bioplastic is defined as biodegradable if it can be decomposed into carbon dioxide under aerobic degradation, or methane and CO2 under anaerobic conditions, inorganic compounds, and new cellular biomass, by the action of naturally occurring microorganisms. This definition however does not provide any information on the environmental conditions, timescale and extent at which decomposition processes should occur. With regard to the aquatic environment, recognized standards have been established to assess the ability of plastics to undergo biodegradation; however, these standards fail to provide clear targets to be met to allow labelling of a bioplastic as biodegradable. Moreover, these standards grant the user an extensive leeway in the choice of process parameters. For these reasons, the comparison of results deriving from different studies is challenging. The authors analysed and discussed the degree of biodegradability of a series of biodegradable bioplastics in aquatic environments (both fresh and salt water) using the results obtained in the laboratory and from on-site testing in the context of different research studies. Biochemical Oxygen Demand (BOD), CO2 evolution, surface erosion and weight loss were the main parameters used by researchers to describe the percentage of biodegradation. The results showed a large variability both in weight loss and BOD, even when evaluating the same type of bioplastics. This confirms the need for a reference range of values to be established with regard to parameters applied in defining the biodegradability of bioplastics.

Treatment of wastewater using Black Soldier Fly larvae: Effect of organic concentration and load.

Recent studies have investigated the use of Black Soldier Fly (BSF) larvae as a promising biological treatment process for high organic content wastewater (i.a. Leachate from municipal solid waste landfill, food processing effluents), achieving both high treatment efficiency and production of secondary resources from larval biomass (i.a. Proteins and lipids). The present study was aimed at achieving a better understanding of how organic concentration and load might influence treatment performance. Larvae were fed with three artificial wastewaters characterised by same organic substances quality (degree of biodegradability and oxidation of the organic content measured respectively as BOD/COD and TOC/COD ratios) but different organic concentrations. Each type of wastewater was tested at four different loads. Treatment performance was assessed by monitoring both larval growth (in terms of weight variation, mortality and prepupation), and variation of wastewater quality and quantity to determine organic substrate consumption (measured in terms of Total Organic Carbon, TOC). Larval starvation was observed in all tests when TOC concentrations dropped below approx. 1000 mg C/L, which, for the tested wastewater, could be assumed as the limit value for adopting BSF larvae process. Substrate concentration in the feed (mgC/L) influenced larval growth (in terms of maximum wet weight, prepupation and mortality) only when organic load was above 10 mgC/larva: the higher the load, the higher the positive impact of the substrate concentration. On the contrary, the specific substrate consumption rate (vS, mgC/larva/day) appeared not to be influenced by substrate concentration but only by the organic load, with a Michaelis Menten like relationship. Accordingly, substrate load can be assumed as a design parameter for BSF treatment process, while substrate concentration might only influence potential resource recovery from larval biomass.

Treatment of food waste contaminated by bioplastics using BSF larvae: Impact and fate of starch-based bioplastic films.

The use of Black Soldier Fly (BSF) larvae in the treatment of biowaste, including food waste, represents a promising new (waste) treatment option. In line with an increasing use of starch-based bioplastics in food packaging, (e.g. shopper films), food waste contamination by these polymers is expected to rise, but the fate of these materials and impact produced on the BSF treatment process remain to be clarified. In the present study, food waste contaminated by starch-based bioplastic film was treated using a BSF larvae process with the aim of investigating both the effect of bioplastics on process performance and the effect of BSF larvae on bioplastic degradation. Larvae treatment performance was assessed by monitoring substrate degradation process and larvae growth in terms of weight variation and development time. Bioplastic degradation (both in the larvae process and in a larvae-free control test) was assessed by means of visual inspection, Scanning Electron Microscopy (SEM), Fourier Transform InfraRed spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and ThermoGravimetric Analysis (TGA). The results obtained highlighted the absence of negative impacts of bioplastics on the BSF process, revealing a modestly higher degree of degradation in the larvae process compared to control test. The process however failed to achieve complete degradation of bioplastics, suggesting the need for additional post-processing treatments.

Washing of residues from the circular economy prior to sustainable landfill: Effects on long-term impacts.

Sustainable landfill continues to play a fundamental role in closing the loop of residual materials of the circular economy. The sustainable landfill relies on both pretreatments and in situ treatments to stabilize the residual waste and immobilize the contaminants, achieving the final storage quality (FSQ) within one generation (typically 30 years). The aim of the study was to investigate the efficiency of the waste washing pretreatment in reducing the waste leaching fraction prior to landfilling, and in decreasing the time needed to reach the FSQ. A laboratory scale washing test was performed on three different kinds of residues from municipal solid waste treatment, usually landfilled: residues sieved from separately collected bio-waste (RB); residues sieved from compost (RC); and residues sieved from mixed waste treatment-plastic line (RP). Column landfill simulation tests were performed to predict and compare the landfill long-term emissions of both washed and raw residues. The results revealed that the washing pretreatment significantly reduced the leachable fraction of contaminants, decreasing the time needed to reach the chemical oxygen demand and ammonia FSQ limits. However, RP residue was the only one respecting the FSQ limits within 30 years.

Treatment of wastewater using black soldier fly larvae, under different degrees of biodegradability and oxidation of organic content.

The biological treatment process based on the metabolism of Black Soldier Fly (BSF) larvae proved to be a highly promising technique for the treatment of high organic content (HOC) wastewater, such as sewage from food industries, leachate from municipal solid waste (MSW) landfill, etc. The present study was aimed at achieving a better understanding of how biodegradability and degree of oxidation of organic content might influence treatment performance and biomass quality. Six leachates characterised by similar COD (Chemical Oxygen Demand) but different BOD5/COD (Biochemical Oxygen demand/COD) and TOC/COD (Total Organic Carbon/COD) ratios were tested. By combining these ratios, the BOD5/TOC ratio was introduced to take into account the effect of both leachate properties (biodegradability and oxidation degree). Process treatment performance was significantly influenced by the quality of organic substances. Higher BOD5/TOC values (higher biodegradability and lower oxidation degree) resulted in a greater and faster larvae growth, with final wet weight of between 49.2 and 91.9mg/larva; lower mortality between 5 and 32%; higher prepupation percentages ranging from 4 to 21% and higher specific substrate consumption rate with values varying from 0.051 to 0.063 mgTOC/mg larva/d, up to 3-fold higher than values obtained using conventional activated sludge based on COD consumption. Conversely, no significant differences were detected in larvae protein and lipid contents, including the profiling of fatty acids.

Preparation of artificial MSW leachate for treatment studies: Testing on black soldier fly larvae process.

When approaching the study of new processes for leachate treatment, each influencing variable should be kept under control to better comprehend the treatment process. However, leachate quality is difficult to control as it varies dramatically from one landfill to another, and in line with landfill ageing. To overcome this problem, the present study investigated the option of preparing a reliable artificial leachate in terms of quality consistency and representativeness in simulating the composition of real municipal solid waste (MSW) leachate, in view of further investigate the recent treatment process using black soldier fly (BSF) larvae. Two recipes were used to simulate a real leachate (RL): one including chemical ingredients alone (artificial synthetic leachate-SL), and the other including chemicals mixed with artificial food waste (FW) eluate (artificial mixed leachate-ML). Research data were analysed, elaborated and discussed to assess simulation performance according to a series of parameters, such as Analytical representativeness, Treatment representativeness (in this case specific for the BSF larvae process), Recipe relevance, Repeatability and Flexibility in selectively modifying individual quality parameters. The best leachate simulation performance was achieved by the synthetic leachate, with concentration values generally ranging between 97% and 118% of the RL values. When feeding larvae with both RL and SL, similar mortality values and growth performance were observed.

Lab tests on semi-aerobic landfilling of MSW under varying conditions of water availability and putrescible waste content.

Semi-aerobic landfilling is applied increasingly as a sustainable technology worldwide, although frequently controversial results are achieved. The authors suggest that differences in water availability (climate, moisture content, etc.) and putrescible waste content are the key factors involved in controlling performance and efficiencies. The aim of the present study was to investigate the effect of inverse conditions (high/low) of these two factors. Six lab-scale lysimeters were specifically set up to correspond to three different conditions of water availability (wet conditions, dry conditions and artificially controlled watering under dry conditions) and two different waste types (high and low putrescible content). Lysimeters were operated for four months under thermal-insulated conditions and the quality and quantity of emissions monitored regularly. Concentrations of mobile ammonia and total organic carbon (TOC) in landfilled waste were modelled by means of first-order kinetics, and carbon and nitrogen mass balances were calculated. The best performance for the semi-aerobic process was achieved at a water availability of approximately 1.5-2.4 kgH2O/kgTS using the following two combinations: a) Waste with high putrescible content and no addition of external water due to the presence of sufficient endogenous water in the waste (moisture) to promote biological stabilisation of waste (Respiration index in 4 days, RI4 = 12.87 mgO2/gTS, BOD/COD < 0.05); b) Waste with low putrescible content and controlled watering (RI4 = 12.25 mgO2/gTS, BOD/COD < 0.04). The study highlighted how semi-aerobic landfilling operations should be carefully adjusted case by case according to waste quality and climate conditions.

The treatment of leachate using Black Soldier Fly (BSF) larvae: Adaptability and resource recovery testing.

The benefits of using Black Soldier Fly (BSF) larvae in biowaste treatment include: commercial value of the stabilized residue, production of biomass rich in fats and proteins, suitable both for biodiesel production and animal feeding. The use of BSF for leachate treatment would introduce a blue low cost solution in the landfill technology, particularly appropriate in developing countries, where landfilling is still widely applied. This paper aimed to investigate the adaptability of BSF larvae to leachate environment, by using different leachate concentrations (25%, 50%, 75%, 100%) and two different feeding substrates: liquid (pure leachate) and semi-solid (wheat bran mixed with leachate). In all tests mortality was less than 50% and it was mainly linked to food shortages: the higher the nutrient content in leachate, the higher the larval development. Dry mass characterisation demonstrate that BSF prepupae biomass can be exploited as an alternative energy source in the production of biodiesel.

Potential treatment of leachate by Hermetia illucens (Diptera, Stratyomyidae) larvae: Performance under different feeding conditions.

In this study, the ability of H. illucens larvae (black soldier fly (BSF)) to metabolise different semisolid biowastes (e.g. kitchen waste, animal manure) has been applied to the treatment of landfill leachate. A testing programme has been developed by mixing leachate with three different solid supports: wheat bran, a biodegradable nutrient substrate, brewers' spent grain, a biodegradable nutrient residue from the brewery industry and sawdust, a low biodegradable residue from the wood industry. Larvae growth rate was monitored in terms of weight variation, mortality and time to reach the prepupal stage. Prepupal biomass composition was analysed in terms of crude protein, lipids and fatty acids. Substrates were monitored at the beginning and the end of tests for total solids (TS), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonia and (whenever significant) the 7-day Respirometric Index (RI7). The best performance was observed with wheat bran and brewers' spent grain, achieving an average larval weight ranging from 155.1 to 226.1 mg (w/w) with prepupation of more than 80% over 21 days. The initial TS, TOC and nitrogen content in feeding substrates had been metabolised (gasified and accumulated in prepupal biomass) by approximately 55%, 60% and 48%, respectively. Dry mass characterisation displayed a significant content of fats and proteins. The analysis demonstrated the suitability of BSF prepupal biomass for the production of biodiesel; however, the potential use of proteins as an animal feed needs further studies for assessing the presence of contaminants.

Innovative dual-step management of semi-aerobic landfill in a tropical climate.

Despite concerted efforts to innovate the solid waste management (SWM) system, land disposal continues to represent the most widely used technology in the treatment of urban solid waste worldwide. On the other hand, landfilling is an unavoidable step in closing the material cycle, since final residues, although minimized, need to be safely disposed of and confined. In recent years, the implementation of more sustainable landfilling aims to achieve the Final Storage Quality conditions as fast as possible. In particular, semi-aerobic landfill appears to represent an effective solution for use in the poorest economies due to lower management costs and shorter aftercare resulting from aerobic stabilisation of the waste. Nevertheless, the implementation of a semi-aerobic landfill in a tropical climate may affect the correct functioning of the plant: a lack of moisture during the dry season and heavy rainfalls during the wet season could negatively affect performance of both the degradation process, and of leachate and biogas management. This paper illustrates the results obtained through the experimentation of a potential dual-step management of semi-aerobic landfilling in a tropical climate in which composting process was reproduced during the dry season and subsequently flushing (high rainfall rate) during the wet period. Eight bioreactors specifically designed: four operated under anaerobic conditions and four under semi-aerobic conditions; half of the reactors were filled with high organic content waste, half with residual waste obtained following enhanced source segregation. The synergic effect of the subsequent phases (composting and flushing) in the semi-aerobic landfill was evaluated on the basis of both types of waste. Biogas production, leachate composition and waste stabilization were analysed during the trial and at the end of each step, and compared in view of the performance of anaerobic reactors. The results obtained underlined the effectiveness of the dual-step management evidencing how wastes reached a higher degree of stabilization and reference FSQ values for leachate were achieved over a one-year simulation period.