Municipal Wastewater Sludge as a Sustainable Feedstock for Upgradeable Renewable Crude Oil via Hydrothermal Liquefaction

Abstract

Every year billion tonnes of municipal wastes are produced in the world. It is expected that by 2025, the municipal waste produce will rise to approximately 2.2 billion tonnes every year. Due to its nature and dangers associated with it becomes a problem to dispose of the waste product. It also contains various bacteria and virus. Municipal waste obtained after passing through various stages of waste water treatment plat (WWTP) can be put to useful purposes like producing oil. A detailed study on municipal waste is carried out with the purpose of converting it into commercially viable oil. There are many alternatives available like pyrolysis, gasification, transesterification, esterification but hydrothermal liquefaction (HTL) has been considered as the most promising path. During HTL, the water is considered as the reaction medium reducing the requirement to dewater the bio-mass which can be a crucial energy input for bio-fuel yield. Initially, various parameters like pH, bulk density, ash-free dry weight, moisture content, CHNS, Calorific Value are characterized. High total carbon and oxygen was observed in the municipal waste samples (29-59%). The ash content lies in the range of 32-52%. The sample MW 4 being fibrous in nature has a very low bulk density, almost similar to that of cotton. The hydrothermal liquefaction of sludge was carried at an elevated temperature (330⁰C) and pressure (200 bar) to disintegrate and form bio-mass macromolecule into bio-fuel. It is successfully separated into solid and liquid with visible oil. The highest yield of product obtained is 82.84% of which 50.78% is solid yield and 32.16% is liquid yield. Oil present in liquid can be easily extracted by centrifugation. There is some oil present in solid which is successfully extracted by the methodology developed. After extraction various tests were done like: Rock Analysis of the sample before and after extraction indicating the loss of hydrocarbons which indicates extraction of the oil. The highest yield of oil extracted is from MW1 (36.2%.) which is considered an appreciable percentage (as per literature) keeping in consideration the feedstock is Municipal wastewater.