Comparative testing of energy yields from micro-algal biomass cultures processed via anaerobic digestion

Although digestion of micro-algal biomass was first suggested in the 1950s, there is still only limited information available for assessment of its potential. The research examined six laboratory-grown marine and freshwater micro-algae and two samples from large-scale cultivation systems. Biomass composition was characterised to allow prediction of potentially available energy using the Buswell equation, with calorific values as a benchmark for energy recovery. Biochemical methane potential tests were analysed using a pseudo-parallel first order model to estimate kinetic coefficients and proportions of readily-biodegradable carbon. Chemical composition was used to assess potential interferences from nitrogen and sulphur components. Volatile solids (VS) conversion to methane showed a broad range, from 0.161 to 0.435 L CH4 g?1 VS; while conversion of calorific value ranged from 26.4 to 79.2%. Methane productivity of laboratory-grown species was estimated from growth rate, measured by changes in optical density in batch culture, and biomass yield based on an assumed harvested solids content. Volumetric productivity was 0.04–0.08 L CH4 L?1 culture day?1, the highest from the marine species Thalassiosira pseudonana. Estimated methane productivity of the large-scale raceway was lower at 0.01 L CH4 L?1 day?1. The approach used offers a means of screening for methane productivity per unit of cultivation under standard conditions

Quantification of methane losses from the acclimatisation of anaerobic digestion to marine salt concentrations

The research assessed losses in methane production as a result of raising digester salt concentrations to marine values, and of increasing the feedstock sulphate concentration. Acclimatisation of inoculum from a municipal wastewater biosolids digester was begun by raising the concentration of chloride salts (Na, Mg, Ca and K) to 6–9 g L?1, as initial experiments showed higher concentrations caused severe inhibition. After stable operation for four retention times salt content in the reactors and the feed was increased by 1 g L?1 every 14 days, up to 31.1 g L?1. The digesters were fed daily in semi-continuous mode and monitored for performance and stability criteria including specific methane production (SMP). SMP was 6–7% less than in controls using the same feedstock without saline addition. After steady-state conditions were achieved at high chloride salinity, magnesium chloride was partially replaced by magnesium sulphate to give a range of sulphate concentrations. Higher sulphate concentrations caused initial instability, indicated by volatile fatty acid accumulation. This subsequently reduced and stable operation was achieved at marine sulphate concentrations, but with a ?5% loss in SMP due to interspecies substrate competition. High sulphate also affected pH, leading to gaseous H2S production proportional to the applied sulphate loa

Increased personal protective equipment litter as a result of COVID-19 measures

Use of personal protective equipment (PPE) increased during the COVID-19 pandemic to reduce virus transmission. Here, we quantitatively analyse emergence of PPE and COVID-19-related litter over 14 months for 11 countries using the litter collection application Litterati. The proportion of masks in litter increased by &gt;80-fold as a result of COVID-19 legislation, from &lt;0.01% to &gt;0.8%. Gloves and wipes, more prevalent at ~0.2% of litter before the pandemic, doubled to 0.4%, but this has since fallen. Glove litter increased in the initial stages of the pandemic but fell after the introduction of facemask policies, whereupon there was an increase of facemask litter. National COVID-19 policy responses and international World Health Organization announcements and recommendations are a probable driver of PPE litter dynamics, especially the implementation of facemask policies. Waste management should be incorporated in designing future pandemic policies to avoid negative environmental legacies of mismanaged PPE.</p