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

## TL;DR

This paper shows how shrimp pond sludge can be turned into valuable products using enzymes from bacteria and photosynthetic bacteria.

## Contribution

A novel sequential bioprocess using enzyme-producing bacterial consortia and photosynthetic bacteria for aquaculture waste valorization.

## Key findings

- Enzyme cocktails reduced sludge solids by 40.1% and increased soluble COD threefold.
- Photosynthetic bacteria produced valuable bioproducts like carotenoids and bacteriochlorophylls.
- The process could be applied to other aquaculture wastes for biovalorization.

## Abstract

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.