The Case for the Biodegradation Pathway

Abstract

With rising energy costs and concerns over global warming, sustainable treatment with a reduced carbon footprint is fast becoming the goal of major wastewater treatment utilities. Sustainability goals are driving the industry to take on the challenge of transforming wastewater treatment from an energy-consuming and waste-producing activity to one with positive net energy production and minimal residuals. Raw wastewater contains ten times the energy needed to treat it (Shizas and Bagley, 2004). However, most of the soluble organic compounds that contribute to the measured energy are mineralized to carbon dioxide or synthesized into new cell matter during treatment. The remaining energy is recoverable from biosolids either as steam or waste heat following thermal processes or as a methane-rich gas following anaerobic digestion. To be able to recover energy from biosolids for meeting energy needs onsite or for electricity generation and to displace the fossil-based energy used is very central to the theme of sustainability. Methods of energy recovery from biosolids are at more advanced stages of development than technologies for energy recovery from the liquid stream. This paper provides an overview of some of the newer thermal conversion technologies and their potential for energy recovery in comparison with the conventional anaerobic digestion pathway.

Employing Energy Management Planning to Achieve Net Zero Energy in Wastewater Operations

“…Therefore, while considering the energy recovery potential from solids and the energy efficiency of a facility, the key is to draw the system boundary around the entire facility rather than just around the solids processes, since the liquid treatment processes could impact the energy recovery potential from biosolids." (Santha, Shimp et al 2010) This opportunity to modify nutrient removal processes has the favorable result of accomplishing "energy autarky," meaning energy self-sufficiency. This treatment approach was explored by Siegrist at plants in Europe.…”

“…If there is interest in using biosolids as a fertilizer for its nutrient value, then the biodegradation pathway is attractive." (Santha, Shimp et al 2010) Thermal processing has several energy balance implications. Santha explains that, with sufficiently high volatile solids and adequate dewatering, thermal oxidation can be sustained without an auxiliary fuel source.…”

“…The total electricity generation potential for this gas use option includes electricity generated onsite and electricity generated using the heat dried product offsite." (Santha, Shimp et al 2010) Pretreatment of wastewater sludges for improved digestion and biogas production was given an extensive review by Dru Whitlock, of CH2M Hill (Whitlock, Sandino et al 2008). He divided the technologies into two types: Processes and Mechanisms (Sonication, Thermal Hydrolysis, Cambi Thermal Hydrolysis Process, BioThelys Process, Homogenization, Pressure Release) and mechanical shearing methods (ABSKady Biolysis Process, Lysate Centrifuge, Pulsed Electric Field).…”