The residence times of plastics in the oceans are unknown, largely because of the durability of the material and the relatively short (decadal) period of time over which plastic products have been manufactured. In this study, classic LEGO bricks constructed of acrylonitrile butadiene styrene (ABS) and washed up on beaches of southwest England have been subjected to X-ray fluorescence (XRF) analysis and the spectra and any other identifiers matched with unweathered blocks stored in collections or sets of known history. Relative to unweathered equivalents, weathered blocks exhibit varying degrees of yellowing, fracturing and fouling, and are of lower mass, average stud height and mechanical strength. These effects are attributed to photo-oxidative degradation and the actions of physical stress and abrasion while exposed to the marine environment. Infrared spectra indicate that the polymer remains largely intact on weathering but with photo-degradation of the polybutadiene phase of ABS, while quantification of XRF spectra reveals that pigments like cadmium sulphoselenide become more heterogeneously distributed in the matrix when in the environment. Using measured mass loss of paired (weathered versus unweathered) equivalents and the age of blocks obtained from storage we estimate residence times of between about 100 and 1300 years for this type and thickness of plastic, with variations reflecting differences in precise additive composition and modes of weathering.

PURPOSE OF REVIEW: Membrane techniques have been employed to concentrate livestock manure effluent from anaerobic digestion to produce highly concentrated liquid organic fertilizer. This review aims to provide a comprehensive understanding on the opportunities and challenges of membrane processes in the concentration of digested effluent for their further implementation. RECENT FINDINGS: Anaerobic digestion has been deployed to convert livestock manure into biogas (energy) and digestate with high potential as biofertilizer. Digestate can be separated into a solid and liquid fraction to reduce required capacity for onsite storage. The liquid fraction, known as digested effluent, remains a vexing challenge to digestate management due to the contradiction between its continuous production and seasonal application to farmlands, particularly in developing countries. Recent investigation has demonstrated the promise of membrane techniques for the concentration of digested effluent to recover recycling water and produce nutrient-rich liquid fertilizer. These techniques mainly include hydraulically driven membrane processes (from microfiltration to reverse osmosis), forward osmosis, membrane distillation, and electrodialysis. In most cases, these membrane techniques are hybridized to enhance the concentration efficiency. Nevertheless, the practical application of these membrane processes is hindered by several technical challenges, which mainly include membrane fouling, contaminant enrichment, ammonia volatilization, and high economic input. In this paper, we critically reviewed the performance of different membrane processes in the concentration of digested livestock manure effluent. Key technical challenges and their potential countermeasures were elucidated. Furthermore, future perspectives were provided to shed light on further development of membrane concentration techniques in the field.

The influence of ultrasonication on membrane performance was investigated by two ultrasonication modes, direct and indirect ultrasonication as pretreatment, and simply improved PVDF-TiO₂ membranes’ performance was systematically compared. Ultrasound intensity of 100% and ultrasonication time ranged from 1 to 2 h positively affect membrane permeability. Characterization results manifested that membrane structure was eventually optimized with an even nano-TiO₂ dispersion by direct ultrasonication. Analysis of surface roughness reflected that PVDF-TiO₂ (MS-U2) surface morphological pattern was peak-valley structure that resisted fouling greatly. A good fitting of experimental result and Tansel’s simulation illustrated that anti-fouling ability was realized direct ultrasonication modified membrane. PVDF-TiO₂ (MS-U2) membrane showing the lowest |τ| reflecting the time required to reach a certain level of the fouling degree was the lowest. Relying upon modified Hermia’s model analysis, protein blockage within the membrane pore was one major fouling mechanism; surface blockage degree of PVDF-TiO₂ (MS-U2) was relative slight. Fouling mechanism analyzed by two models reflected that PVDF-TiO₂ (MS-U2) membrane exhibited a higher anti-protein fouling ability during cross-flow filtration process.

The Gippsland Lakes estuary, a Ramsar listed wetland, in Victoria, Australia, is an area of potential concern for metal pollution due to influxes of human population and associated anthropogenic activities. A biomonitoring exercise was undertaken where the concentrations of 9 metals (Cr, Fe, Cu, Zn, As, Se, Ag, Cd and Hg) were analysed in the soft tissue of two common sessile invertebrates: the mussel Mytilus edulis and the barnacle Amphibalanus variegatus from 6 locations on two different occasions throughout the Gippsland Lakes estuary. A salinity gradient exists in the Lakes, from seawater at Lakes Entrance in the east, decreasing down to < 10 PSU in the west at Lake Wellington during times of rainfall, which is a major factor governing the growth and distribution of both species. Dissolved metal levels in general were low; however, Cu at most sites exceeded the 90% trigger values, while all Zn concentrations exceeded the lowest 80% trigger values of the ANZECC marine water quality guidelines for environmental health. Elevated levels of Cu and Zn were found particularly in barnacles at some sites with environmental contamination due to leaching from anti fouling paints and sacrificial zinc anodes. Elevated levels of Ag and Cd were found in mussels at the Hollands Landing site, which is immediately adjacent to a boat ramp, and Cd and Ag at this site are suspected to originate from inland anthropogenic sources. Concentrations of As in M. edulis across all 6 sites in both sampling periods had mean wet weight As concentrations exceeding the maximum level stated in the FSANZ guidelines. A. variegatus contained elevated levels of Hg especially at the North Arm site with a maximum of 13.6 μg Hg/g dry wt., while A. variegatus also showed temporal changes in Hg concentrations across sites. The maximum Hg concentration found in Mytilus edulis was 1.49 μg Hg/g dry wt. at the Hollands Landing site. Previous contaminant studies of biota in the Lakes have targeted sampling of singular predatory or migratory species, such as Black Bream (Acanthopagrus butcheri) and the Burrunan dolphin (Tursiops australis). This is the first biomonitoring study conducted on sessile organisms to assess metal contamination in the system.

The effect of hydraulic retention time (HRT) and sludge retention time (SRT) on extracellular polymer substrate (EPS) content and resistance of a hybrid membrane bioreactor (HMBR) treating domestic sewage was analyzed by Box-Behnken response surface methodology. The quadratic response surface model demonstrated significant effects of both HRT and SRT on EPS content (both P value < 0.05), SRT on membrane resistance (P value = 0.0119), and their interaction was significant (P value = 0.0273) for EPS but not membrane resistance (P value = 0.0609). Model optimization indicates that the optimal conditions for the HMBR to control membrane fouling were an HRT of 10 h and SRT of 30 days. Under these optimal conditions, both the EPS content and the predicted membrane resistance closely matched the actual average value with the error about 8%. Thus, the feasibility of applying response surface methodology to an HMBR for treating domestic sewage was demonstrated. According to the detection result of the three-dimensional fluorescence (excitation-emission matrix), humic acid-like and fulvic acid-like substances gain much higher levels in the suspended carriers than those in the membrane and sludge, suggesting that these are key components of the membrane pollutants. Graphical abstract .

A submerged anaerobic membrane bioreactor (SAnMBR) was used to treat low-concentration domestic sewage. The effects of hydraulic retention time (HRT) and organic load (OLR) on chemical oxygen demand (COD) removal, methanogenesis, and membrane fouling of the system were investigated. The SAnMBR achieved good COD removal efficiency as well as stable methane production, which were significantly affected by both OLR and HRT. The influent dissolved organic matter (DOM) was decomposed and transformed over time, and DOM concentration was gradually reduced. It can be inferred that the SAnMBR can effectively intercept the production of extracellular polymeric substances and improve effluent quality. The phenomenon of membrane fouling was investigated using various analytical tools. Results demonstrated that the SAnMBR was achieved good transmembrane pressures (TMP) (10–15 kPa), and the hydraulic force generated by the stirring device has a dynamic physical shearing action on the surface of the membrane, which can partly alleviate membrane fouling.