A novel approach to anaerobic groundwater treatment: Mitigating the effect of methane on the biological stability of drinking water

A novel approach to anaerobic groundwater treatment: Mitigating the effect of methane on the biological stability of drinking water

Wessels, P.H.

Van der Meer, W.G.J. (mentor)
Grefte, A. (mentor)
Prest, E.I.E.D. (mentor)
Van der Laan, H. (mentor)

Civil Engineering and Geosciences

Water Management

Sanitary Engineering

2014-11-20

Oasen has set itself the goal to “produce water of an impeccable quality and to delivery it flawlessly to its customers”. In formulating this goal, Oasen expresses its concern for unknown pollutants and the increasing concentrations of organic micro-pollutants in its source waters (primarily anaerobic groundwater). To achieve this goal, the company has devised a new treatment approach which is first to be implemented at an outdated treatment plant called ZS de Hooge Boom by 2018. The new approach centres on Reverse Osmosis (RO) as a primary barrier against pollutants, treating the anaerobic groundwater directly after abstraction. RO is followed by ion exchange (IEX) columns to remove remaining ammonium and a remineralisation step which is used to add calcium and magnesium. After these three treatment steps, the water is still anaerobic and contains methane (2700 ?g/L CH?). An additional step, capable of removing sufficient amounts of methane to produce biologically stable water, had to be designed. In contrast to conventional treatment, where part of the methane is broken down biologically in sand filters, the removal had to be achieved by a single aeration system. Additionally, experts expected large quantities of biomass to be produced on even very small concentrations of methane, which would lead to biological instability. There is however no legislation on the allowable concentration of methane and there was till now, no direct assay quantifying the effect of methane on the biological stability in drinking water. Two questions, therefore had to be answered: How much methane should be removed in order to produce biologically stable water? Which (aeration) system is most optimal to achieve this concentration? Growth potential tests were carried out on batches of samples containing various concentrations of methane. The yields of methane-oxidising bacteria (MOB) were calculated and the difference in cell volume between MOB and AOC bacteria (from control sample) was analysed. The results show that the yield of MOB on methane falls in the range of 8.6 x 10?-1.7 x 10? cells/?g CH? and that there is a factor 2 cell volume difference between MOB and AOC bacteria. Since the yield of bacteria on AOC is known (1x10? cells/?g AOC) the following bulk parameter for biological stability was derived: Bulk GP=C_AOC +C_(?CH?_4 )/Y_f =C_AOC +C_(?CH?_4 )/2.7 [?g AOC eq./L] This parameter takes into account the cell yields and the difference in cell volume so that the resulting value is a measure of the bio-volume produced on a certain amount of AOC and CH? and expresses this in AOC equivalents. With Oasen’s treatment approach, the AOC content is expected to be very low (<1 ?g/L) so that with an effluent methane concentration of 10 ?g/L, the bulk GP <5 ?g AOC eq. /L. Three aeration systems were tested in a pilot plant: Tower Aerators, Plate Aerators and Membrane Contactors. The latter has never been used for large scale drinking water treatment or the removal of methane. The three systems were tested for removal efficiency, a conceptual design was made and costs and energy consumption were estimated. Where necessary the gaps were filled with information found in literature. Having tested all three systems, a multi-criteria analysis was performed, in which it was determined that Tower Aerators are the most optimal treatment technique for the sufficient removal of methane in order to guarantee biological stability at Kamerik.

methane removal
drinking water
biological stability
bulk growth potential

http://resolver.tudelft.nl/uuid:90ae773c-17f5-416c-b58d-de2937f458ed

Student theses

master thesis

(c) 2014 Wessels, P.H.