An integrated novel plasma-microalgae approach for landfill leachate treatment using a high-ammonia tolerant strain of Chlorella vulgaris

Landfilling is the most common method worldwide to deal with the produced municipal solid wastes (MSW). Nonetheless, one major drawback of landfilling is the production of landfill leachate (LL). Various methods for LL treatment exist which can mainly be divided into biological and physical-chemical methods, however integrating both approaches result in more effective treatment. In this study, an indigenous Chlorella vulgaris was isolated from a landfill leachate treatment site, purified, and genetically identified for leachate treatment purposes. One replicate, C.V.M* (CCAP 211/141), of the tested Chlorella vulgaris showed an outstanding growth in 20 % LL (v/v) with a significant ammonia removal (p < 0.05). To confirm these findings, both of the Chlorella vulgaris replicates (C.V.M* and C.V.N) were further tested in 20 % LL (v/v). A dramatic increase in the growth of C.V.M* by 19-fold over its peer C.V.N with a 75 % ammonia removal (starting from concentration 290.73 mg/L) was observed. This percentage is further improved when injecting plasma activated microbubbles as a pre-treatment step. The plasma pre-treatment resulted in LL decolourisation after 3 h and reduced ammonia-N concentration by 1.9-fold. C.V.M* showed the highest growth in 20 % LL pre-treated by plasma compared to the untreated LL with a final biomass yield of 0.38 g/L, increase in the total ammonia-N removal (79 %) and a significant decrease in the pH value (8.6-6.67). Whole genome sequencing for both replicates revealed differences in genotypes between them which might indicate the possibility of a developed mutation or sexual reproduction that might have increased the ability of replicate/strain C.V.M* to tolerate harsher conditions and higher ammonia-N concentrations in 20 % diluted LL. These results might pave the way for a possible powerful candidate in LL treatment using a high-ammonia tolerant algal strain which when coupled with plasma pre-treatment might provide an effective, eco-friendly, and sustainable LL treatment approach.