Optimization of H2 Production through Minimization of CO2 Emissions by Mixed Cultures of Purple Phototrophic Bacteria in Aqueous Samples

I.A Vasiliadou,F Martinez,J.A Melero,R Molina,D Puyol

doi:10.3390/w12072015

Abstract

One of the current challenges in the treatment of wastewater is the recovery and/or transformation of their resources into high value-added products, such as biohydrogen. The aim of the present study was to optimize the production of hydrogen by mixed cultures of purple phototrophic bacteria (PPB), targeting in low CO2 emission. Batch assays were conducted using different carbon (malic, butyric, acetic acid) and nitrogen (NH4Cl, Na-glutamate, N2 gas) sources by varying the chemical oxygen demand to nitrogen ratio (COD:N 100:3 to 100:44), under infrared radiation as sole energy source. Malate-glutamate (COD:N 100:5.5) and malate-NH4-N (COD:N 100:3) fed cultures, exhibited high H2 production rates of 2.3 and 2.5 mLH2/Lh, respectively. It was observed that the use of glutamate decreased the CO2 emission by 74% (13.4 mLCO2/L) as compared to NH4-N. The H2 production efficiency achieved by organic carbon substrates in combination with glutamate, was in the order of malic (370 mLH2/L) > butyric (145 mLH2/L) > acetic acid (95 mLH2/L). These substrates entailed partitioning of reducing power into biomass at 64%, 50% and 48%, respectively, whereas reductants were derived to biohydrogen at 5.8%, 6.1% and 2.1%, respectively. These results suggest that nitrogen source and carbon dioxide emissions play an important role in the optimization of hydrogen production by PPB.

Highlights

Nowadays, human activities associated with food production, agriculture, domestic and industry generate considerable amounts of waste effluents rich in nutrients and organic compounds.Uncontrolled disposal of these wastes alters severely the biogeochemical cycles of the global ecosystems and can cause great damage to the environment
These results suggest that nitrogen source and carbon dioxide emissions play an important role in the optimization of hydrogen production by phototrophic bacteria (PPB)
This study aims to evaluate the performance of mixed PPB cultures for biohydrogen production from wastewater, while minimizing CO2 emissions

Summary

Introduction

Human activities associated with food production, agriculture, domestic and industry generate considerable amounts of waste effluents rich in nutrients and organic compounds. Uncontrolled disposal of these wastes alters severely the biogeochemical cycles of the global ecosystems and can cause great damage to the environment. Public or private associations responsible for water sanitation invest lot of energy in wastewater treatment plants just for the destruction of organic matter and removal of nutrients, in order to avoid the contamination of water bodies. The use of photosynthetic organisms for partitioning of resources from wastewater has received considerable attention worldwide, since is an environmental-friendly and a low energy alternative, compared to physical separation processes, such as membrane technologies [1,3]. Microalgae have been widely used for nutrients’ partitioning from the liquid into their solid phase from wastewater, they form macroscopic structures that hinders their settleability, which makes hard their

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