Study on the safe disposal and resource utilization of cyanobacterial bloom biomass in Dianchi Lake, China

Abstract

To solve the problem of utilizing massive harmful algal blooms (HABs) biomass, we developed a technique involving physical purification methods, namely, microfiltration (2 μm, 0.45 μm), ultrafiltration (100 kDa cutoff), and low-temperature precipitation (4 °C, 48 h), as the core methodology and used the toxic Microcystis biomass in Dianchi Lake for batch preparations of microcystins (MCs) and phycocyanin (PC). The results were as follows: (1) From 1.0 kg of Dianchi Lake cyanobacteria, 57 g of PC powder with a purity (A 620 /A 280 ) of 1.78 was prepared. An acute oral toxicity test in mice showed that the LD 50 of the prepared PC was >5.25 g kg −1 , practically non-toxic. The LD 50 of PC administered by intraperitoneal injection was >4.71 g kg −1 . The Ames test showed that the mutagenic effect was negative independent of the addition of S9. The overall results of the toxicity tests suggested that the prepared PC was not potentially toxic. (2) From 666.7 g of cyanobacteria, 2.262 g of MC extract powder (containing 192.7 mg of MC-RR and 54.3 mg of MC-LR) was prepared. MC-RR and MC-LR accounted for 8.52% and 2.40%, respectively, and the extraction ratios for MC-RR and MC-LR were 40.1% and 83.1%, respectively. A further purification by preparative HPLC was carried out, obtaining 2.338 mg of pure MC-RR (chromatographic purity >85%) from 70 mg of MC extract powder, which was used as an HPLC chromatographic standard and in routine toxicology experiments. The efficiency of the ultrafiltration treatment of cyanobacterial powder reached 49.3 kg d −1 , and the cost of producing food-grade PC powder in this study was 17.6 US$ g −1 , which is only 13.6% of the current price of food-grade PC on the international market. Thus, the cost advantage was significant. Therefore, this study provides an approach for the safe disposal of HABs and the large-scale commercial utilization of HAB biomass.