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Currently lime water is dosed for final water pH correction at a client's WTW. This lime water system is unable to achieve the additional pH correction required to counteract a proposed fluoride dose and so sodium hydroxide dosing is required (and is struggling with achieving required pH at...

I am wanting to confirm the impact on pH of sodium bisulphite being added to water. To do so, I need to calculate the number of H ions liberated when sodium bisulphite (NaHSO3) is added to water. For example, I know for ferric chloride the reaction is FeCl3+3H20 ⇌ Fe(OH)3+ 3H+ + 3Cl- i.e. 3...

Has anyone experienced pH dropping across GAC filters? The filters have been installed alleviate problems with pesticide in drinking water. Since commissioning the filters, the pH has been dropping from 8.3 at the inlet to as low as pH7.2 at outlet. One theory is development of a biological...

Hello, I've been asked by a client about the possibility of cleaning RGF Calder nozzles which have been blocked with manganese deposits and whether it would be possible to clean these nozzles with a DWI "Acid" / Chemical on the market (Which is DWI approved) that could clean / remove / dissolve...

I've seen in a number of reports an equation to work out a theoretical ferric or alum dose for coagulation. The formulas go something like this.... Alum Dose (as Al2(SO4)3.18H20) in mg/l = 17.8 + 0.295 x Colour (°H) + 5.41(pH - 7) [Mean Turbidity + Mean Colour] x 0.08 x 2 x 3.6 = mg/l as...

Thanks bimr. All those precautions are already incorporated in the design. I take it that the main issue with off-gassing from sodium hypochlorite is the potential for inadequate doisng or pipe blockages? Do many chemicals have the potential to off-gas?

I'm working on a WTW upgrade at the moment and would appreciate some advice. A new secondary treatment building is to be constructed with chemical storage tanks being located below ground level. One of the chemicals to be stored in these tanks is sodium hypochlorite. A concern has been raised...

A lot of guidance I've read for sludge production refers to highly turbid & highly coloured raw waters. What would people consider the limit above which a raw water source could be considered highly turbid or coloured. For colour, I was thinking over 100 Hazen but I've seen raw waters with...

Thanks bimr. When it's shown like that, it's obvious it won't make a difference. It also illustrates how such a small volume of chemical can have an effect on a much larger volume of water.

Thanks bimr. With regards to dilution, my question is this: It's 22% sodium hydroxide being dosed. The required dosing flowrate and sizing of the dosing pumps is calculated on the main treatment flowrate, the dose (mg/l) required to raise the pH of the water and the % strength of the sodium...

The way I understand it now is that there can be a number of reasons why “carrier water” is used: • to actually help carry along the water i.e. to make sure the dosed chemical achieves a certain velocity range e.g. so lime powder doesn’t come out of solution and block dosing lines • to ensure...

Hello, I've been asked for advise regarding the range of acceptable pipeline velocities for pumping sludge generated at a WTW. I've had an internet trawl and have been through the usual textbooks (MWH, Twort) to see whether I could find any details. Most specs give guidance for wastewater...

Thanks for everyone's advice. Much appreciated!

Hello all, As part of a WTW upgrade, we're changing from chlorine gas to sodium hypochlorite. The sodium hypochlorite dosing requires carrier water to maintain velocity in the dosing lines. This carrier water is final water from the WTW and as such has been dosed with sodium hydroxide. At a...

I'm currently working on an upgrade to an existing water treatments. Part of the upgrade includes new chemical storage and dosing equipment. Sodium Hypochlorite and Orthophosphoric Acid are both to be dosed at the same point in the treatment train (this is currently the case and they are both...

I'm currently designing a set of GAC contactors for pesticides (MCPA) removal at an existing water treatment works and was hoping someone could provide me with their thoughts on the following The water authority currently installs GAC contactors as standalone units between primary and secondary...

Hi Guys, I'm working as process engineer on the design of a set of manganese rapid gravity filters at an existing WTW with upstream DAF & RGFs. I've been tasked with confirming likely headloss through these secondary filters so we can confirm hydraulics. The primary filtered water will be dosed...

Thanks bimr. The water authority's specification requires a static mixer and from previous discussions are reluctant to grant waivers from this. The site is fairly tight for size and it would be approx only 0.3 m from dose point to limestone contactor. Would this give sufficient mixing in your...

I’m working on a project for a water company upgrading a UF/MF water treatment membrane treatment works. Currently hypo is dosed post membrane direct into the pipeline followed by pH correction through a limestone contactor. As part of the upgrade, the hypo would be dosed into a static mixer...

Thanks bimr. Why would we expect more particulate iron breakthrough when using caustic? In what way would coagulation need adjusting? I believe jar tests have been carried out to confirm coagulation pH. I can't see why coagulation pH would change just because caustic is used instead of lime...