Removal of phosphate by the green seaweed Ulva lactuca in a small-scale sewage treatment plant (Ios Island, Aegean Sea, Greece)

In the present study, the use of seaweeds for phosphate absorption was examined as a tertiary treatment in sewage treatment plants, to improve the water quality and reduce eutrophication risks. The data came from both laboratory and field experiments that took place on Ios Island sewage treatment plant. Three different macroalgae were tested and Ulva lactuca was finally chosen thanks to its high survivability in low salinity waters. Since the main restrictive factor was low salinity, we initially established the ratio of seawater:effluent that combined satisfactory viability with maximum phosphate absorption. The biomass growth under these conditions was also examined. Based on the above results, we designed a continuous-flow system with a 1/4 volume per hour water turnover, in a mixture of 60% sewage effluent: 40% sea water and 30 g L-1 initial biomass of U. lactuca that must be renewed every 10 days. Under these conditions and time frame, the phosphate content of the effluent was reduced by about 50%. © Springer Science+Business Media B.V. 2009

Herd immunity acquired indirectly from interactions between the ecology of infectious diseases, demography and economics

Patterns of morbidity and mortality around the globe are determined by interactions between infectious diseases and systematic human socioeconomic processes. The most obvious of these patterns is that the greatest burdens of infectious diseases are found among the poor, who lack the basic resources for disease prevention and treatment. Yet, it is becoming increasingly clear that many infectious diseases are themselves causes of poverty owing to their effects on labour productivity. A particularly subtle phenomenon that receives little attention in the epidemiology literature and is especially important for poor communities is the role of the birth rate as an important direct cause of high disease burdens. Because of their high rates of transmission and life-long immunity, the persistence of many child diseases such as measles relies on high rates of reproduction as their source of susceptible individuals. Thus, there are significant direct health benefits of lower fertility rates, which are further enhanced by interactions with economic processes. Indeed, fertility, poverty and disease all interact with each other in important and predictable ways that can be built into traditional disease ecology models. We present such a model here that provides insights into the long-term effect of policy interventions. For example, because of indirect income effects, herd immunity may be acquired with lower vaccine coverage than previously thought. Reductions in the disease burden can also occur through lower fertility. Our model thus provides a disease ecology framework that is useful for the analysis of demographic transitions

Combustion behavior of algal biomass: carbon release, nitrogen release, and char reactivity

Recent focus on algae biomass as an alternative energy source can be attributed to building pressure for conservation of dwindling fossil fuels and reduced greenhouse gas emissions. Both micro- and macroalgae have many advantages over terrestrial plants, including typically faster growth rates and, therefore, higher rates of carbon fixation. This paper reports the combustion characteristics of a species of microalgae and two species of macroalgae under conditions that are relevant for the large-scale use of biomass for heat and other products. The tested species were Tetraselmis sp. (marine microalgae), Derbersia tenusissima (marine macroalgae), and Oedogonium sp. (freshwater macroalgae). Two variants of Oedogonium were tested. One variant was cultivated using standard nutrient additions, and the other variant was starved of essential nutrients. Carbon conversion to CO and CO2 and the release of N as NO were determined for the algae by oxidizing fixed-bed samples of each alga in air at 800 and 1000 °C. The gasification reactivity of the chars was also characterized by gasifying samples of each alga in a thermobalance in pure CO2 (1 atm) at 800 °C, following in situ devolatilization of the algal samples. Carbon conversion to CO and CO2 exceeded 84% for all of the tested algae. Most of the fuel C was released during fuel devolatilization, consistent with the proximate analysis for these fuels. Nitrogen conversions to NO ranged between 6 and 12 g of N/100 g of fuel N for Tetraselmis, 6–9 g of N/100 g of fuel N for Derbersia, and 11–21 g of N/100 g of fuel N for the two Oedogonium variants, with NO emissions occurring mainly during devolatilization, in most cases. Chars produced from samples of macroalgae were much more reactive than the chars from the microalgae, most likely because of the inhibitory effects on mass transfer caused by the very high ash content of the sample used in the present study. The reactivities of all chars increased at high char conversions

Enhanced production of green tide algal biomass through additional carbon supply

Intensive algal cultivation usually requires a high flux of dissolved inorganic carbon (Ci) to support productivity, particularly for high density algal cultures. Carbon dioxide (CO2) enrichment can be used to overcome Ci limitation and enhance productivity of algae in intensive culture, however, it is unclear whether algal species with the ability to utilise bicarbonate (HCO3−) as a carbon source for photosynthesis will benefit from CO2 enrichment. This study quantified the HCO3− affinity of three green tide algal species, Cladophora coelothrix, Cladophora patentiramea and Chaetomorpha linum, targeted for biomass and bioenergy production. Subsequently, we quantified productivity and carbon, nitrogen and ash content in response to CO2 enrichment. All three species had similar high pH compensation points (9.7–9.9), and grew at similar rates up to pH 9, demonstrating HCO3− utilization. Algal cultures enriched with CO2 as a carbon source had 30% more total Ci available, supplying twenty five times more CO2 than the control. This higher Ci significantly enhanced the productivity of Cladophora coelothrix (26%), Chaetomorpha linum (24%) and to a lesser extent for Cladophora patentiramea (11%), compared to controls. We demonstrated that supplying carbon as CO2 can enhance the productivity of targeted green tide algal species under intensive culture, despite their clear ability to utilise HCO3−