Sustainability Evaluation of Immobilized Acid-Adapted Microalgal Technology in Acid Mine Drainage Remediation following Emergy and Carbon Footprint Analysis.

Kuppan Praveen,Mallavarapu Megharaj,Kadiyala Venkateswarlu,Sudharsanam Abinandan

doi:10.3390/molecules27031015

Kuppan Praveen, Mallavarapu Megharaj + Show 2 more

Open Access

https://doi.org/10.3390/molecules27031015

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Abstract

Sustainability evaluation of wastewater treatment helps to reduce greenhouse gas emissions, as it emphasizes the development of green technologies and optimum resource use rather than the end-of-pipe treatment. The conventional approaches for treating acid mine drainages (AMDs) are efficient; however, they need enormous amounts of energy, making them less sustainable and causing greater environmental concern. We recently demonstrated the potential of immobilized acid-adapted microalgal technology for AMD remediation. Here, this novel approach has been evaluated following emergy and carbon footprint analysis for its sustainability in AMD treatment. Our results showed that imported energy inputs contributed significantly (>90%) to the overall emergy and were much lower than in passive and active treatment systems. The microalgal treatment required 2–15 times more renewable inputs than the other two treatment systems. Additionally, the emergy indices indicated higher environmental loading ratio and lower per cent renewability, suggesting the need for adequate renewable inputs in the immobilized microalgal system. The emergy yield ratio for biodiesel production from the microalgal biomass after AMD treatment was >1.0, which indicates a better emergy return on total emergy spent. Based on greenhouse gas emissions, carbon footprint analysis (CFA), was performed using default emission factors, in accordance with the IPCC standards and the National Greenhouse Energy Reporting (NGER) program of Australia. Interestingly, CFA of acid-adapted microalgal technology revealed significant greenhouse gas emissions due to usage of various construction materials as per IPCC, while SCOPE 2 emissions from purchased electricity were evident as per NGER. Our findings indicate that the immobilized microalgal technology is highly sustainable in AMD treatment, and its potential could be realized further by including solar energy into the overall treatment system.

Highlights

The present study evaluated the sustainability of immobilized acid-adapted microalgal system for bioremediation of acid mine drainages (AMDs) by comparing with active treatment system (ATS) and passive treatment system (PTS) following emergy and carbon footprint analysis
Emergy analysis showed that renewable energy input was extremely low in the case of the microalgal treatment system, the total emergy value was lower than in other treatment systems
This was consistent with emergy indices, with higher Environmental loading ratio (ELR) value and lower per cent renewability than for PTS and ATS

Summary

Introduction

The efficacy of treatment processes including precipitation, adsorption, electrochemistry, and membrane filtration is influenced by low pH and the presence of high metal concentrations [4]. Significant efforts have been made to promote an energy-efficient and ecologically friendly wastewater treatment system for AMD [6]. In addition to pollutant removal and achieving the effluent discharge requirement, environmental consequences of chemical and energy consumption, and greenhouse gas (GHG) emissions created by the wastewater treatment process attracted more attention from the environmental scientists [7]. Microalgal technology aids in wastewater treatment, and provides significant environmental, economic, and social advantages by reducing chemical consumption and net pollutant emissions [11,12,13,14]

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