Growth kinetics and competition between Methanosarcina and Methanosaeta in mesophilic anaerobic digestion.

Methanosarcina species with a high maximum specific growth rate (mumax) and high half-saturation coefficient (KS) and Methanosaeta species with a low mumax and low KS are the only known aceticlastic methanogens. Because of Methanosaeta's low KS, the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were measured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion.     

Public Perceptions of California's Exceptional Drought

While the exceptional drought in California ended in 2017, the state is expected to experience similar droughts in the future. Understanding how individuals perceive the causes and consequences of drought will help frame future communication and planning efforts. We surveyed a panel of Californian residents about their perceptions of the 2012–2017 drought. We found a major disconnect in how our respondents perceived drought and water use. Respondents perceived the drought as being caused primarily by climatic factors and underestimated the role human water use, particularly agricultural use, had in exacerbating drought. Comparing our respondents across the state and across socio‐demographics, there were few differences in concern about drought but several differences in how residents thought drought should be managed. Such research can help water managers communicate about the specific concerns the public has about future droughts, as well as address misperceptions about the relationship between drought and water use.     

Effects of oxygen exposure on anaerobic digester sludge.

Recuperative thickening of anaerobic digester sludge (thickening with solids return) yields increased digester capacity. Common thickening methods cause oxygen exposure to the digester sludge. This study evaluated the effects of various levels of oxygen exposure on the acetoclastic methanogens. Gravity belt thickening had no detrimental effect on the acetoclastic activity. From a 7-day batch test with continuous oxygen exposure of digester sludge, a 12% loss in acetoclastic activity was predicted for a digester with a 20-day solids retention time (SRT) and 100% recycle with recuperative thickening via dissolved air flotation thickening. However, a greater loss (27%) was found from a long-term, bench-scale digester operated under similar conditions. This loss did not affect the digester performance, as measured by volatile solids destruction. This research suggests that recuperative thickening may not affect digester performance at a long SRT with constant operation, but may change the reserve capacity of the anaerobic community.     

Statistical evaluation of the influence of flow conditions and sampling techniques on water quality data.

The purpose of this study is to statistically evaluate the influence of various sampling methodologies and flow conditions on the quality and comparability of total phosphorus concentration data collected over the course of 27 months at the South Florida Water Management District (SFWMD) S-65E structure. The data was obtained from the following sampling methodologies: U.S. Geological Survey (USGS) (Reston, Virginia) equal width increment spatially composite grab samples, USGS replicate samples, SFWMD grab samples, and SFWMD autosampler samples. Both significant and insignificant differences were reported from these comparisons. Parametric and nonparametric standard statistical tests for significance were carried out to evaluate the differences between the data. To avoid invalid conclusions of insignificant differences, we conducted tests for equivalence of the means and variances. The results from the data analysis revealed that both flow conditions and sampling methodology affected the water quality data.     

Relationship between dietary phosphatidylcholine and serum cholesterol in the lobster Homarus sp.

The absence of soy phosphatidylcholine (PC) in purified diets fed to juvenile lobstrs causes a significant decrease in the concentrations of total cholesterol and phospholipids in the serum. When egg PC, bovine PC, phosphatidylinositol, and ovine cephalin are used as substitutes for the soy PC, cholesterol and phospholipid levels in the serum are also significantly reduced. Cholesterol and phospholipid concentrations in the serum are highly correlated. Analysis of levels of hepatopancreatic cholesterol indicate that intestinal absorption of cholesterol is not impaired by the absence of dietary PC or by the presence of a phospholipid substitute. We suggest that the PC molecule is an important component of a lipoprotein complex that effectively transfers cholesterol, an essential nutrient for lobsters, from the hepatopancreas to the hemolymph.This work is a result of research sponsored in part by NOAA, Office of Sea Grant, Department of Commerce, under Grant No. 04-8-MO1-189 R/A 28. The US Government is authorized to produce and distribute reprints for governmental purposes notwithstanding any copyright notation that may appear hereon     

Evaluating landfill disposal of chromated copper arsenate (CCA) treated wood and potential effects on groundwater: evidence from Florida

Chromated copper arsenate (CCA) treated wood has been used for more than 50 years. Recent attention has been focused on appropriate disposal of CCA-treated wood when its service life ends. Groups in the US and Europe concerned with the possibility of arsenic migration to groundwater from disposed CCA-treated wood have proposed that consumers be required to dispose of the wood as a hazardous waste, in the most protective of landfills. We examined available data for evidence of arsenic migration from unlined construction and demolition (C&D) debris landfills in Florida, where CCA-treated wood is disposed. Florida was chosen because soil, groundwater, landfill design, weather, and levels of CCA-treated wood use make the state a uniquely sensitive indicator for observing arsenic migration from CCA-treated wood disposal sites, should it occur. We developed and quality-checked a CCA-treated wood disposal model to estimate the amount of wood and associated arsenic disposed. By 2000, an estimated 13 million kg of arsenic in CCA-treated wood was disposed in Florida; however, groundwater monitoring data do not indicate that arsenic is migrating from unlined C&D landfills. Our results provide evidence that highly stringent regulation of CCA-treated wood disposal, such as treatment as a hazardous waste, is unnecessary.