Comparison of different cultures and culturing conditions for the biological deterioration of organic load from real saline bilge wastewater: microbial diversity insights and ecotoxicity assessment

Abstract

Bilge wastewater is a high strength, typically saline wastewater, originating from operation of ships. In this study, the treatment of real bilge wastewater was tested using pure isolated aerobic strains and mixed cultures (aerobic and anaerobic). The Chemical Oxygen Demand (COD) and ecotoxicity decrease were monitored over time, while the microbial dynamics alterations in mixed cultures were also recorded. The isolated strains Pseudodonghicola xiamenensis, Halomonas alkaliphila and Vibrio antiquaries were shown to significantly biodegrade bilge wastewater. Reasonable COD removal rates were achieved by aerobic mixed cultures (59%, 9 days), while anaerobic mixed cultures showed lower performance (34%, 51 days). The genus Pseudodonghicola was identified as dominant under aerobic conditions both in the mixed cultures and in the control sample (raw wastewater), after exposure to bilge wastewater, demonstrating natural proliferation of the genus and potential contribution to COD reduction. Biodegradation rates were higher when initial organic load was high, while the toxicity of raw wastewater partially decreased after treatment.

Untapped Potential of Moving Bed Biofilm Reactors with Different Biocarrier Types for Bilge Water Treatment: A Laboratory-Scale Study

“…For the quantification of chemical oxygen demand in bilge wastewater, the closed reflux, colorimetric method was used, as proposed by standard methods [29]. In order to take into consideration the oxidation of chloride ions, an appropriate modification to the method occurred, as described in a previous study [8]. The absorbance of digested samples was measured at 600 nm or 420 nm using a portable spectrophotometer (Hach DR1900).…”

“…In reactors R1a and R2, where operational parameters were identical but the type of biocarrier differed (K3 in R1a and Mutag BioChip in R2), 82.8 ± 2.7% and 78.7 ± 5.1% COD removal, respectively, was recorded. Reactor R1b (treating R1a effluent) recorded low removal efficiency (18.7 ± 10.2%), probably due to low inflow COD (R1b inflow: 1060 ± 65 mg L −1 ) and due to the low BOD 5 :COD ratio that this wastewater type presents [8]. During the second hydraulic and organic load shock (B) (HRT: 3 days in each reactor; inflow COD: 9051 ± 83 mg L −1 ), 86.6 ± 0.5% and 61.1 ± 3.0% COD removal for Systems A and B, respectively was recorded.…”

“…From all collected samples, total genome DNA was extracted in our laboratory using the genomic DNA kit for stool samples (NucleoSpin DNA Stool). For Batch 1, the sequencing analysis was performed by DNASense (Denmark), as described in a previous work [8]. For Batch 2, the sequencing analysis was performed by Novogene Europe (UK), and the main analysis steps are summarized below.…”

“…R1a again recorded higher removal efficiency than R2 (69.4 ± 5.8% vs. 61.1 ± 3.0%), and during this period the removal efficiency of R1b was significant (54.5 ± 9.6%), while its inflow COD was 2761 ± 65 mg L −1 . The abiotic degradation of the examined wastewater was investigated in a previous study [8], indicating that no significant COD deterioration could occur in the absence of microbial activity. Therefore, biodegradation is considered to be the main removal mechanism of the wastewater's organic load.…”

“…Furthermore, the complexity of this wastewater type may alter over time, as different operational or maintenance activities may occur on the vessel. With these particularities, it is hard to establish a biological treatment process with competent and stable performance, either in onshore facilities or aboard a vessel [6,8]. Though bilge wastewater is a highly toxic type of wastewater [8], its biodegradation has been studied in the past, pointing out several isolated strains and groups of microorganisms involved in the process [8][9][10][11][12][13].…”