Enhancement of Hydrolysis and Biogas Production of Primary Sludge by Use of Mixtures of Protease and Lipase

Sequential Bioprocesses for Biovalorization of Shrimp Pond Sludge by Hydrolytic Enzymes-Producing Bacterial Consortia and Photosynthetic Bacteria

This study aimed to valorize shrimp pond sludge through sequential bioprocesses using hydrolytic enzyme cocktails produced by bacterial consortia, and photosynthetic bacteria. The production of enzyme cocktails by a co-culture of protease-, amylase-, and lipase-producing bacteria (PAL) was performed in a 5-L stirred tank bioreactor using a low-cost medium. The crude enzyme cocktails were concentrated and used to treat shrimp pond sludge. The addition of enzyme cocktails at 2.0 U/ml based on protease activity led to a reduction of total suspended solids by 40.1% and an increase in soluble chemical oxygen demand (COD) by 3 folds. The solubilized nutrients from shrimp pond sludge in liquid fraction were used as a sole nutrient source to cultivate a newly isolated photosynthetic bacteria (PSB) identified as Rhodocista pekingensis. This PSB was able to grow and achieve a high biomass of 1.30 ± 0.28 g/l and produce value-added bioproducts including aminolevulinic acid (11.77 ± 0.55 μM), carotenoids (166.84 ± 0.03 mg/g dry cell weight), and bacteriochlorophylls (771.47 ± 0.17 mg/g dry cell weight). These results highlight the potential use of enzyme cocktails produced by the co-culture of hydrolytic bacteria to facilitate the biovalorization of aquaculture sludge by PSB and may also greatly contribute to biovalorization of other similar aquaculture wastes into valuable bioproducts.

Performance evaluation of biocatalytic and biostimulation approaches for the remediation of trace organic contaminants in municipal biosolids

Trace organic contaminants (TrOCs) in biosolids is creating potential threats for reuse of biosolids. Out of the tested 64 trace organic contaminants, seven pharmaceutically active compounds (PhACs), and three pesticides were detected in biosolids from a municipal wastewater treatment plant. This study encompasses the removal of TrOCs and improvement in the aerobic digestion of biosolids by various pretreatments including utilization of indigenous microbes present in biosolids (T1), the effect of an enzymatic pretreatment (T2), biostimulation by the addition of an external carbon source (T3) and the synergic effect of biostimulation and enzymatic pretreatment (T4). After 28 days of aerobic digestion, total PhACs removal was 44% with T1, which improved to 51%, 54% and 62% in T2, T3 and T4, respectively. Also, total pesticides removal was 10% in T1, which enhanced to 44%, 14% and 54% in T2, T3 and T4, respectively. The extracellular enzyme activities were also monitored in all the treatments and the maximum activities (114 ± 11 U/L lipase, 382 ± 29 U/L phosphatase, 155 ± 8 U/L protease, 304 ± 26 U/L amylase, 108 ± 7 U/L laccase, and 63 ± 2 U/L lignin peroxidase) were observed in T4 after 28 days of digestion. Thus, this study aids in providing changing aspects of enzyme profiles during these processes and the enhanced bioremediation of biosolids through the hydrolytic and oxidoreductase enzymes produced by the indigenous microorganisms.