Time Course of Carbonaceous BOD₅, COD, Phosphorus and Ammonium in Baghdad Sewage Inoculated with A Tigris River Chlorella-Like Isolate: Paired Microcosm Experiments
DOI:
https://doi.org/10.59675/P422Keywords:
Microalgae, Wastewater Treatment, CBOD₅, COD, Orthophosphate.Abstract
Background: Microalgae are a potentially viable option for supplemental wastewater treatment, but oxygen-demand and phosphorus responses vary with strain, wastewater and incubation time, and, to our knowledge, time-resolved multi-indicator data with matched controls are scarce for Iraqi isolates.
Objective: To quantify the effect of a Tigris River Chlorella-like isolate (TR-CV-01) on carbonaceous BOD₅ (CBOD₅), COD, soluble COD, soluble reactive phosphorus (SRP), total phosphorus (TP), ammonium-N and biomass over 14 days in Baghdad sewage, and to test with bacteria-only, heat-killed and axenic controls whether the algae are responsible.
Methods: Experiment 1 used three independent batches and 54 flasks of autoclaved sewage at three strengths. Experiment 2 used four batches from two plants (two batches per plant), two matrix types, five treatments, duplicate flasks and six destructive sampling days (0–14; 480 flasks). For Experiment 2, duplicate flasks were averaged within a batch, and the batch was the inferential unit (n = 4), not the individual flask.
Results: In Experiment 1, inoculated flasks differed from paired controls by −5% in CBOD₅ on day 1, −16% on day 7 and −25% on day 14; total COD was 11% lower, soluble COD 31% lower, SRP 24% lower (day-14 CI −48 to +10), ammonium-N 22% lower and VSS 93% higher, while TP was essentially unchanged (+2%). In Experiment 2, live non-axenic TR-CV-01 on day 14 reduced CBOD₅, COD, soluble COD, SRP and NH₄-N by 27.7%, 25.4%, 31.4%, 53.6% and 48.6%, respectively, in autoclaved sewage; the corresponding reductions in non-sterile sewage were 11.3%, 12.9%, 16.5%, 25.9% and 26.5%. TP was 3.2% higher in autoclaved sewage and 0.2% higher in non-sterile sewage relative to controls. Axenic-algae versus bacteria-only contrasts supported an algal contribution. Biomass P represented approximately 96% and 80% of the net live-versus-control SRP changes in autoclaved and non-sterile sewage, respectively; this approximate comparison is not a closed phosphorus mass balance. Phosphorus concentrations are reported as mg/L P.
Conclusions: TR-CV-01 was associated with lower oxygen demand and dissolved-nutrient indicators in batch microcosms. Experiment 1 tested autoclaved sewage from one plant; Experiment 2 extended the comparison to autoclaved and non-sterile sewage at 100% strength from two plants, with smaller live-culture effects in non-sterile sewage. These results do not establish full-scale treatment performance. CBOD₅ bottle pH handling in Experiment 2 is described from the bottle-level records: pH was measured, and 1 N H₂SO₄ was added to bottles marked as adjusted; the records do not support a single pH threshold for deciding which bottles were adjusted. Phosphorus concentrations are reported as mg/L P.
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