Peter F. Strom

There is considerable confusion about ‘bioplastics.’ They are often touted as ‘greener’ than conventional plastics and may be claimed to be biodegradable and compostable. However, there are a great variety of different products claimed to be bioplastics, and they differ greatly in many characteristics. In this review, we discuss the large diversity of bioplastic products derived from biological materials and compare their various physio-chemical characteristics with conventional (petroleum-derived) plastics. We define a number of terms that are often confused or ambiguous. We examine the biodegradability of different bioplastics in various environments (e.g. higher or lower temperatures, composting, soil, freshwater, seawater) and the byproducts (e.g. chemicals, microplastics) that they may release during degradation. In addition, we review studies that evaluated the toxicity of the products released, including toxicity to cell lines and bacteria, to plants, and to terrestrial and aquatic animals. Many studies have compared toxicity of bioplastics with conventional plastics. The diverse bioplastics differ greatly in toxicity. Furthermore, toxicity test methods employed have been varied—some studies have tested solid pieces of plastic, some have used microplastics generated from the bioplastic, and some have used plastic product leachates. The reviewed studies have used different conventional plastics to compare bioplastics with. Many studies found that the bioplastics were more toxic than the conventional plastics. Therefore, it is impossible to draw any overall conclusions that ‘bioplastics’ as a group are more or less toxic than conventional plastics, but it would be incorrect to conclude that they are in general more ‘environmentally friendly.’

Reed beds with Phragmites australis (common reed) have been utilized to decrease the water, nutrient, and volatile solids content of sewage sludge. An efficient disposal/reuse option was sought for reed bed biosolids accumulated over a 15-year period at a wastewater treatment facility in New Jersey, USA. The study facility had 14 reed beds, each with 1000 wet tons capacity, which were full, and so the solids needed to be removed. Because P. australis is considered an invasive species in New Jersey and several other states in the United States, disposal or reuse of solids containing this plant is regulated. Composting was examined as a potential treatment for destroying the plant's reproductive rhizomes. The high temperatures achieved during composting were also tested to determine if regulatory criteria for pathogen reduction could be met, making the composted product suitable for unrestricted land application. Preliminary studies indicated the sludge had stabilized to the point where self-heating did not occur. Among the carbon amendments tested in the laboratory to stimulate compositing activity, Phragmites above-ground biomass was determined to be most suitable. In a field test, Phragmites above-ground biomass was mixed with reed bed biosolids at a 1:2 (w/w) ratio. The temperatures achieved resulted in complete mortality of Phragmites rhizomes. In laboratory tests, rhizomes placed in a drying oven at 50°C for 24 h, or 55°C for 12 h, showed 100% plant mortality. However, under field conditions pile temperatures could not be maintained long enough for the sludge to meet the USEPA 503 biosolids time-temperature pathogen rule requirements for unrestricted land application, even though sample fecal coliform counts did meet regulatory limits.

Leachate from mixed glass cullet (crushed recycled glass containers) that is stockpiled before use as construction aggregate or sand substitute is a potential source of water pollution. Rainwater leaching through the stockpiles dissolves and suspends organic compounds and nutrients from the glass. The objectives of this study were to investigate the effect of forced aeration on leachate quantity and quality in the glass cullet stockpiles compared to mechanical turning/mixing. Three experimental stockpiles were set up in the field, two with forced aeration treatment (one with fine and the other with coarse cullet) and one (coarse cullet) with mechanical turning. The organic concentrations in the leachate in most cases were comparable to those of raw domestic wastewater. Organic constituents (e.g., BOD5 ) were reduced by>70% from the initial levels ( ∼450 mg L−1 ) during a 1.5-month period with forced aeration, compared to an 85% decrease in the turned stockpile. Particle size affected temperature and oxyg...

A full‐scale, closed‐loop bioreactor (Orbal oxidation ditch, Envirex brand technologies, Siemens, Waukesha, Wisconsin), previously examined for simultaneous biological nutrient removal (SBNR), was further evaluated using computational fluid dynamics (CFD). A CFD model was developed first by imparting the known momentum (calculated by tank fluid velocity and mass flowrate) to the fluid at the aeration disc region. Oxygen source (aeration) and sink (consumption) terms were introduced, and statistical analysis was applied to the CFD simulation results. The CFD model was validated with field data obtained from a test tank and a full‐scale tank. The results indicated that CFD could predict the mixing pattern in closed‐loop bioreactors. This enables visualization of the flow pattern, both with regard to flow velocity and dissolved‐oxygen‐distribution profiles. The velocity and oxygen‐distribution gradients suggested that the flow patterns produced by directional aeration in closed‐loop bioreactors created a heterogeneous environment that can result in dissolved oxygen variations throughout the bioreactor. Distinct anaerobic zones on a macroenvironment scale were not observed, but it is clear that, when flow passed around curves, a secondary spiral flow was generated. This second current, along with the main recirculation flow, could create alternating anaerobic and aerobic conditions vertically and horizontally, which would allow SBNR to occur. Reliable SBNR performance in Orbal oxidation ditches may be a result, at least in part, of such a spatially varying environment.

Based on the International Water Association's (London) Activated Sludge Model No. 2 (ASM2), biochemistry rate expressions for general heterotrophs and phosphorus‐accumulating organisms (PAOs) were introduced to a previously developed, three‐dimensional computational fluid dynamics (CFD) activated sludge model that characterized the mixing pattern within the outer channel of a full‐scale, closed‐loop bioreactor. Using acetate as the sole carbon and energy source, CFD simulations for general heterotrophs or PAOs individually agreed well with those of ASM2 for a chemostat with the same operating conditions. Competition between and selection of heterotrophs and PAOs was verified using conventional completely mixed and tanks‐in‐series models. Then, competition was studied in the CFD model. These results demonstrated that PAOs and heterotrophs can theoretically coexist in a single bioreactor when the oxygen input is appropriate to allow sufficient low‐dissolved‐oxygen zones to develop.

Horse manure and cranberry fruit (5:1) amended with cow manure were composted in duplicate 25 m³ piles for 252 days. Piles were mixed and aerated with a front loader. Temperature was recorded at up to 80 points in each pile; it reached 74°C on day 7, and averaged >45°C through day 157. Oxygen content was measured 7 times at 27 points in each pile up to day 31, and varied from 0.1 to 13%. Volume and total mass reductions achieved were 73% and 71%, respectively, despite the addition of water on 3 occasions. The quality of the product, horse manure cranberry fruit compost (HCC), was examined on samples removed periodically from each pile and analyzed for pH, moisture, volatile solids, total carbon, nitrogen species, chemical oxygen demand of a water extract (COD), cation exchange capacity, and the ratios C/N, COD/N, C/NH₄⁺-N, and COD/NH₄⁺-N. The biodegradation kinetics for dry mass followed a nearly first order decay (k= 0.0187 kg/kg-day). Fecal streptococci, used as an indicator of sanitation, were reduced by >4 log-units. Phytotoxicity tests performed on aqueous compost extracts found decreasing sensitivity for seeds in the order: arabidopsis ≈ lettuce » tomato > wheat > cucumber, corresponding with seed size and food reserve capacity. The germination index (GI) improved with composting time. Multiple regression analysis between GI and physical-chemical parameters revealed that ammonia concentration was the most influential chemical factor affecting (negatively) germination. Samples of composting material taken at 31, 157 and 252 days were assessed as container plant growth media alone and combined with commercial Promix (1:1). Seedlings emerged and grew faster in the Promix and Promix:HCC compared with HCC alone, and plants grew poorest in the young HCC alone.

There is an increased interest in composting manure on small horse farms (1-5 horses). It is known that simple backyard, food waste composters do not efficiently reduce pathogens due to their small scale. However, it was not clear if small-scale manure composting on horse farms could ensure pathogen reduction during all seasons. Furthermore, because of potential human health concerns, the release of Aspergillus fumigatus on small horse farms was of interest. The objective of this study was to evaluate pathogen reduction in a simple shed composter and the release of Aspergillus fumigatus emissions from fall to spring under typical farm operational conditions. Horse manure mixed with wood shavings (bedding) was composted for 4-8 weeks in the fall, winter, early spring and late spring. Fecal streptococci and eggs of strongyles, which are a major recognized health concern for horses, were used as pathogen indicator organisms. Temperatures increased in all composting piles during all seasons, but tended to be higher in warmer weather. After 4 weeks, the fecal streptococci reduction was about 10- to 100-fold and, after 8 weeks, about 100- to 1000-fold. There was some effect of season on fecal streptococci levels, with the higher composting temperatures appearing to provide greater reductions. Strongyle eggs in this study were very low and were reduced over time. Levels of viable A. fumigatus spores during turning ranged from 12-2084 CFU m⁻³, while background levels ranged between 6 - 300 CFU m⁻³. Overall, this study indicates that composting horse manure mixed with wood shavings reduces pathogens. A. fumigatus levels are elevated during turning, but the levels are lower than those found at sewage sludge/municipal solid waste composting facilities or inside barns.