Wastewater treatment is an energy‐intensive process and a net emitter of greenhouse gas emissions. A large fraction of these emissions is due to intensive aeration of aerobic bacteria to facilitate break‐down of organic compounds. Algae can generate dissolved oxygen at levels in excess of saturation, and therefore hold the potential to partially displace or complement mechanical aeration in wastewater treatment processes. The objective of this study was to develop an internally consistent experimental and modeling approach to test the hypothesis that algal photosynthetic aeration can speed the removal of organic constituents by bacteria. This framework was developed using a simplified wastewater treatment process consisting of a model bacteria (
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Abstract Escherichia coli ), a model algae (Auxenochlorella protothecoides ), and a single carbon source that was consumable by bacteria only. This system was then tested both with and without the presence of algae. A MATLAB model that considered mass transfer and biological kinetics was used to estimate the production and consumption of O2and CO2by algae and bacteria. The results indicated that the presence of algae led to 18–66% faster removal of COD by bacteria, and that roughly one‐third of biochemical oxygen demand was offset by algal photosynthetic aeration. -
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Abstract BACKGROUND Insect biomass is a sustainable alternative to traditional animal feeds, particularly when insects are produced on low‐value high‐volume agricultural by‐products. Seven samples of almond by‐product (hulls and shells) were obtained from processors in California and investigated for larvae production. Experiments were completed with and without larvae and spent substrate samples were assessed for their potential as soil amendments based on standard compost quality indicators.
RESULTS On average, specific larvae growth and average larval harvest weight were 158% and 109% higher, respectively, when larvae were reared on Monterey and pollinator hulls compared to nonpareil hulls and mixed shells. Larvae methionine and cystine contents were highest when larvae were reared on Monterey hulls and mixed shells, respectively. Available phytonutrients in spent substrate were affected by feedstock sample and larvae rearing. Spent nonpareil substrate without larvae had the highest NH4‐N levels and spent pollinator substrate incubated without larvae had the highest PO4‐P levels. Spent mixed shell substrate had the lowest availability of phytonutrients.
CONCLUSION The findings demonstrate that by‐product composition has a significant impact on larvae growth and the properties of the spent substrate, and that spent substrate from larvae rearing requires further stabilization before application as a soil amendment. © 2020 The Authors.
Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
