Optimizing accuracy and efficacy in data-driven materials discovery for the solar production of hydrogen

The production of hydrogen fuels, via water splitting, is of practical relevance for meeting global energy needs and mitigating the environmental consequences of fossil-fuel-based transportation. Water photoelectrolysis has been proposed as a viable approach for generating hydrogen, provided that stable and inexpensive photocatalysts with conversion efficiencies over 10% can be discovered, synthesized at scale, and successfully deployed (Pinaud et al., Energy Environ. Sci., 2013, 6, 1983). While a number of first-principles studies have focused on the data-driven discovery of photocatalysts, in the absence of systematic experimental validation, the success rate of these predictions may be limited. We address this problem by developing a screening procedure with co-validation between experiment and theory to expedite the synthesis, characterization, and testing of the computationally predicted, most desirable materials. Starting with 70 150 compounds in the Materials Project database, the proposed protocol yielded 71 candidate photocatalysts, 11 of which were synthesized as single-phase materials. Experiments confirmed hydrogen generation and favorable band alignment for 6 of the 11 compounds, with the most promising ones belonging to the families of alkali and alkaline-earth indates and orthoplumbates. This study shows the accuracy of a nonempirical, Hubbard-corrected density-functional theory method to predict band gaps and band offsets at a fraction of the computational cost of hybrid functionals, and outlines an effective strategy to identify photocatalysts for solar hydrogen generation

Quality of vegetables in Ghanaian urban farms and markets

This chapter shows results obtained from analyzing samples of vegetables taken at the farm gate and from selling points in Accra, Kumasi and Tamale. Microbiological data are based on a total of about 1,500 vegetable samples taken from different sampling points along the vegetable distribution chain – farm gates – and from different categories of sellers in Accra, Tamale and Kumasi. Fecal coliforms and helminth eggs were mainly used as the fecal contamination indicator organisms. For chemical contaminants, heavy metals and pesticides in irrigation water and vegetables were analyzed, while estrogens were used as an example for emerging contaminants

Quality of irrigation water used for urban vegetable production

This chapter presents findings from studies conducted in Accra, Kumasi and Tamale aimed at assessing the quality of irrigation water used by farmers in and around the cities. Samples for laboratory analysis were taken from sources of water used for irrigation. Microbiological, chemical and other emerging contaminants are presented

Quality of vegetables in Ghanaian urban farms and markets

This chapter shows results obtained from analyzing samples of vegetables taken at the farm gate and from selling points in Accra, Kumasi and Tamale. Microbiological data are based on a total of about 1,500 vegetable samples taken from different sampling points along the vegetable distribution chain – farm gates – and from different categories of sellers in Accra, Tamale and Kumasi. Fecal coliforms and helminth eggs were mainly used as the fecal contamination indicator organisms. For chemical contaminants, heavy metals and pesticides in irrigation water and vegetables were analyzed, while estrogens were used as an example for emerging contaminants

Serum estrogenicity and biological responses in African catfish raised in wastewater ponds in Ghana

Reuse of wastewater for aquaculture improves the efficient use of water and promotes sustainability but the potential effects of endocrine disrupting compounds including estrogens in wastewater is an emerging challenge that needs to be addressed. We examined the biological effects of wastewater-borne estrogens on African catfish (Clarias gariepinus) raised in a wastewater stabilization pond (WSP) of a functioning municipal wastewater treatment plant, a wastewater polishing pond (WWP) of a dysfunctional treatment plant, and a reference pond (RP) unimpacted by wastewater, located in Ghana. Measurements of estrogen concentrations in pond water by liquid chromatography/tandem mass spectrometry showed mean 17 s-estradiol concentrations were higher in the wastewater ponds (WWP, 6.6 ng/L ? 2.7 ng/L; WSP, 4.9 ng/L ? 1.0) than the reference (RP, 3.4 ? 1.1 ng/L). Estrone concentrations were found to be highest in the WSP (7.8 ng/L ? 1.7) and lowest in the WWP (2.2 ng/L ? 2.4) with the RP intermediate (4.7 ? 5.0). Fish serum estrogenicity assayed by ESCREEN was significantly higher in female vs. male catfish in the RP and WSP but not in the WWP (p = 0.05). Histological examination of liver and gonad tissue showed no apparent signs of intersex or pathology in any ponds. The similarities in various measures of body indices between fish of this study and African catfish from other freshwater systems suggest that aquaculture may be a suitable reuse option for treated municipal wastewater

Challenges to wastewater aquaculture: a case study of traditional and emerging contaminant concentrations in African catfish [Abstract only]

Municipal wastewater-fed aquaculture promotes efficient water use, however, the potential effects of wastewater-borne traditional and emerging contaminants on fish and human health are potential challenges. The pathogen and heavy metal accumulation in fish tissue and serum estrogenicity and biological effects of wastewater-borne estrogens were assessed in African catfish (Clarias gariepinus) raised in a wastewater stabilization ponds (WSP) of a functioning municipal wastewater treatment plant and reference ponds (RP) unimpacted by wastewater, located in Ghana (West Africa). Preliminary results showed that significantly higher levels (2-3 log units) of pathogen (E. coli) contamination were detected in the gut and skin of fish from the WSP than the reference ponds (p = 0.05). Furthermore, the levels of heavy metals found in fish tissue were below the expected daily nutritional requirement (1-2 mg) for humans and poses insignificant toxicological risks. The mean estrogen concentrations were higher in the wastewater ponds than the reference and fish serum assayed by E-SCREEN showed significantly higher estrogenicity in female vs. male catfish in the RP compared to the WSP (p = 0.05). Histological examination of liver and gonad tissues showed no apparent signs of intersex or pathology. These studies showed that catfish cultivated at the study sites were safe for human consumption, however, precautions such as depuration and effective processing methods including grilling and smoking prior to consumption are recommended to reduce pathogen loads. In terms of fish health, biological metrics in this study suggest that aquacultural use of adequately treated municipal wastewater had minimal estrogenic effects on African catfish. Investigation of other growth and reproduction-modulating compounds (e.g. androgens) are needed