Pretreatments for enhancing sewage sludge reduction and reuse in lipid production

Abstract

Background Converting 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. Results In 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. Conclusion It 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.

Methane yield response to pretreatment is dependent on substrate chemical composition: a meta-analysis on anaerobic digestion systems

“…2). These pretreatments are effective in breaking down organic matter and increasing its exposure to enzymatic degradation during the hydrolysis step 19 . Heat pretreatments are one of the most applied in full-scale biogas plants 9 , which may be a result of the mandatory pasteurization requirement for some substrates.…”

“…Appropriate pretreatment can mitigate the AD instability associated with high loads of waste lipids by improving the dispersion and solubilization of lipids in the sludge matrix 19 . Nevertheless, our results suggest that optimizing the balance of substrates and nutrient ratios via co-digestion could be more promising than investments in pretreatments.…”

“…Here, mixed substrates are those in which carbohydrates, lipids, and proteins are roughly equal without major disproportions between their contents. Although food waste, sewage, and co-digestion comprise a mixture of several organic sources, food waste seems to be the most suitable to be used as a model, since co-digestion prioritizes geographical location and stabilization of organic matter without the addition of pretreatment 45 while the sewage is often pointed out as lipid-rich 19 .…”

Recent Advances in using Lipomyces starkeyi for the Production of Single-Cell Oil

“…lipid accumulation on the pretreated sludge on cultivation with L. starkeyi was 36.67% g/g, 18.42%, 21.08% and 26.31% for ultrasonication pretreatment, acid pretreatment, a l ka l i n e p ret re at m e nt a n d m i c rowave pretreatment, respectively. 64…”

Shrimp Oil-Enriched Mayonnaise Prepared Using Fish Myofibrillar Protein as a Substitute for Egg Yolk: Physical, Rheological, and Sensory Properties

“…FMP can adhere to fat globules by forming a strong protein layer at the interface through various configurations such as train, loop, and tail. FMP as an emulsifier shows potential in developing stable emulsions, aiding in the delivery of nutraceutical and bioactive compounds [12]. FMP, especially from underutilized species with low market value, can serve as an effective emulsifier and texture modifier in mayonnaise formulations.…”