Pretreatments for enhancing sewage sludge reduction and reuse in lipid production

Jiaxin Chen,Xiaolei Zhang,Ji Li,Zhaoyang Wu

doi:10.1186/s13068-020-01844-3

Jiaxin Chen, Xiaolei Zhang + Show 2 more

Open Access

https://doi.org/10.1186/s13068-020-01844-3

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Abstract

BackgroundConverting wastewater sludge to lipid is considered as one of the best strategies of sludge management. The current problem of lipid production from wastewater sludge is the low yield (0.10–0.16 g lipid/g dry sludge) due to the low availability of easily uptaken materials (such as soluble monosaccharide and oligosaccharide) in sludge to oleaginous microorganism (Rhodotorula glutinis, Trichosporon oleaginosus, Lipomyces starkeyi). Pretreatments are efficient methods to improve sludge bioavailability. This study is aimed to achieve high lipid production from sludge and high sludge reduction.ResultsIn this study, it was observed that the soluble chemical oxygen demand (SCOD) had significantly increased after different pretreatment. The SCOD in the supernatant was increased from 32.64 to 180.25 mg/L, 924.16 mg/L, 1029.89 mg/L and 3708.31 mg/L after acidic (pH 2 for 2 h), alkaline (pH 12 for 2 h), microwave irradiation (15 min with 5 min interval), and ultrasonication (30 min at 450 W and 20 kHz frequency with 5 s on and 2 s off mode) pretreatment, respectively. Pretreatments have also increased the release of total nitrogen (TN) and total phosphorus (TP) from solids. The sludge after different pretreatments were used as a medium for lipid production, and the highest lipid content (36.67% g/g) was obtained in the fermentation with ultrasonication pretreatment sludge, and the sludge reduction was 63.10%. For other pretreatments, the lipid content and sludge reduction were 18.42% and 32.63% in acid pretreatment case, 21.08% and 36.44% in alkaline pretreatment case, and 26.31% and 43.03% in microwave pretreatment case, respectively.ConclusionIt was found that ultrasonication pretreatment was the most efficient way to increase the sludge biodegradability (SCOD) and to release TN and TP from solid phase to liquid phase. Pretreated sludge for lipid production achieved significant improvement in lipid yield and sludge reduction. Lipids produced from pretreated sludge were transesterified to biodiesel and the analysis showed that biodiesel had a similar composition as commercial biodiesel. The study reveals that pretreatment on sludge is a promising method for enhancing biological sludge management efficiency.

Highlights

Converting wastewater sludge to lipid is considered as one of the best strategies of sludge management
Pretreatment impact on soluble chemical oxygen demand and nutrient release from sludge Soluble chemical oxygen demand (SCOD) was found to be a reliable character to represent the soluble organics in the liquid phase
It can be seen that the SCOD in the supernatant before pretreatment was 32.64 mg/L (Fig. 1)

Summary

Introduction

Converting wastewater sludge to lipid is considered as one of the best strategies of sludge management. Along with the development of society, wastewater discharge amount sharply increases due to human activities [14]. It was 26.10 billion tonnes in 2004 and dramatically increased to 51.00 billion tonnes in 2014. Carbon recovery from sludge is generally accomplished through direct extraction or converting it to value-added products [13]. Lipids, extracellular polymeric substances, bioplastics, short-chain fatty acids are common value-added products generated from sewage sludge [34, 39, 63]. It provides new option for sludge management and resource recycling [1]

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