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 <i>Rhodocista pekingensis</i>. 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.