Optimal extraction and characterization of alginate-like extracellular polymers (ALE) and proteins from wastewater sludge

Sludge is mainly a complex mixture of proteins, alginate-like extracellular polymers (ALE) and other substances. The content of protein and ALE in sludge is high and widely used, so this study extracted these two high-quality and high-value substances to fully realize the resourcefulness of sludge. In this paper, five extraction methods of ALE were compared and analyzed, and the best extraction method was confirmed: acid coagulation + dialysis method. Based on this method, two extraction paths of protein and ALE were designed: ALE-PN (ALE was extracted first and protein was extracted later) and PN-ALE (protein was extracted first and ALE was extracted later). Through further analysis, the extraction path with better effect is confirmed: ALE-PN. The effect of different extraction methods on the nature of ALE in sludge was first investigated. The purity of acid coagulation method is higher, and the extraction amount of calcium coagulation ion exchange method is higher. By comparing the extraction amount, purity and properties of the five methods, acid coagulation + dialysis method is the best choice of ALE extraction methods. The extraction amount of protein was higher in both paths, but the extraction amount and purity of ALE were lower in the PN-ALE. The protein and ALE extracted from the two pathways contain the characteristic peaks of amino and uronic acid. The proportion of secondary structure and the composition of amino acids of proteins extracted from the two pathways were consistent. Alginate can be judged as a Newtonian fluid, and the ALE extracted by both paths is close to a nonNewtonian fluid (shear thinning). The proportion of three segments in ALE (continuous mannouronic acid unit: GG, continuous gururonic acid unit: MM, alternating unit: GM) is as follows: MM > GG > GM. In conclusion, the extraction effect of ALE-PN is better.