Session 25 - Wastewater treatment

Isolation of microorganisms that can biodegrade organic compounds which are present in olive mill waste and more specifically microorganisms that can survive at high phenol concentrations was studied in the Environmental Engineering Laboratory for three months in the Department of Environmental Science and Technology in the Cyprus University of Technology. Firstly, liquid crops were created, then the samples were cultivated in solid crops (with phenol as the sole carbon source) and at last isolation and purification of the samples were performed and the single colonies were replicated in liquid crops to check their performance. Eight single microbial culture will be sent to Macrogen The Nederlands Research Center for recognition and identification.

Anaerobic ammonium oxidation (anammox) has been considered a promising alternative to the traditional nitrification/denitrification process to remove nitrogen without using external carbon source. The start-up of the anammox process was performed in a stirred anaerobic up-flow reactor seeded with aeration tank sludge, and fed with medium containing ammonium and nitrite (1:1). The reactor was running consecutively for 369 days, with an initial instability period that lasted 117 days, resulting in nitrite removal and nitrate accumulation. In view of this, the reactor stopped being fed with nitrite, which led to a nitrate decrease in the effluent. Afterwards, a 140 days transition period was followed by a 112 days stable period. In the end, the average ammonium removal was 53.8 % in the transition stage, slighting decreasing to 45.6 % in the stable period, while there was no nitrite in the effluent. Preliminary microbial assessment showed the presence of an anammox community in the reactor related to Candidatus ‘Brocadia fulgida’. The next challenge will be the assessment of eventual shifts on the microbial community structure and composition during the entire process.

The discovery of anaerobic ammonium oxidation (anammox) revealed the existence of a shortcut in the classic nitrogen cycle where ammonium is converted directly to dinitrogen gas. The anammox process can be used to develop more cost and energy-efficient sustainable nitrogen removal systems comparing to those existing today. However, large-scale applications are limited due to the slow growth rate of anammox bacteria described so far. The UNNOWN project proposes to explore the presence of these bacteria in different ecological niches, and select the appropriate seeding sludge starter as the inoculum for reactors. Anammox biomass is enriched in batch experiments as well as in laboratory scale bioreactor systems, such as Up-flow Biofilter, and Anaerobic Baffled Reactor. Afterwards, microbial community composition, optimum growth conditions, and nitrogen removal efficiency are studied. The ongoing project aims to investigate new anammox bacteria, and the relation between community structure and process activity. Ultimately, it is planned to develop microbial inocula to be used as seeding sources for anammox reactors, and to contribute to a wider
application of anammox process in wastewater treatment.

The combination of constructed wetlands (CWs) and microbial fuel cells (MFCs) has emerged in recent years with the purpose of enhancing wastewater treatment efficiency of CWs while simultaneously generating electricity. Taking the above into account, the aim of this study is to evaluate the influence of MFC integration on organic matter and nutrient removal in a constructed wetland. The results showed that NH4+-N concentration reduced from 66.5 ±9.4 at day 0 (influent) to 4.5±0.4 mg/L and 7.03±3.93mg/L for the integrated system and control system, respectively. In terms of the NH4+-N removal efficiency, an enhancement of the nitrification rate (Ni) was observed when MFC was integrated in VSSF (120.6±1.5 mg/m2 d for control system and 166.8±2.3 mg/m2 d for integrated system). The average COD removal efficiencies were 85.36±2.67% and 94.2±5.9% in the CW and CW-MFC, respectively, obtaining a voltage close to 250 mV. The maximum power density generated was 4.75 mW/m2. In conclusion, the removal efficiencies of COD and NH4+-N in VSSF were 85.4 and 88.4%, respectively, while in CW-MFC were 94.3 and 93.2 %. Therefore, the integrating of a MFC into CW does not have adverse effects on the capacity of the CW to efficiently domestic wastewater treatment.

Ozonation was studied as a pretreatment method for a waste biological sludge, contaminated with large amounts of globally used antibiotics; tiamulin, levofloxacin and amoxicillin. At the concentrations of over 100 mg L-1, these antibiotics were found to inhibit biogas production (up to 50%), which means, that the molecules would pass the anaerobic digestion system unchanged. Ozonation of sludge, contaminated with antibiotics, not only removes inhibitory effects, but also improves overall biogas production for 10% or even more, depending on the dose of the oxidant applied in the pretreatment.