Case Study- Chemical Free Iron Removal.
BREAKWAVE MURWILLAMBAH RD , QLD .
Author: Helmut Dresselhaus – Pacific Water Technology – Brisbane
Pacific Water Technology recently commissioned a new commercial water treatment facility for bore water to produce high quality water destined for the water bottling plants in Queensland. The innovative technology employed is leading edge, and has delivered excellent results. The project included the complete scope from equipment design, supply of equipment and storage tanks, as well as commissioning and process optimisation.
In order to ensure that the good properties of this water is maintained during storage, the 316 Stainless Steel tanks from Select Water Tanks provided the cost effective solution. The water bottlers require very strict water quality standards, both in regards to chemical and microbiological standards exceeding Australian Drinking Water Guidelines. The best technology and equipment was therefore selected to ensure optimum results are delivered. A secondary concern was the formation of bromate due to the ozone oxidation of bromide. Due the low levels of bromide (less than 30 ppb) there was undetectable levels of bromate.
The table below compares the results of ozonation vs aeration of the water, both delivering results well within the required tolerances. There was some evidence of perhaps ozone oxidation causing some manganese to go back into solution, however this can be remedied by reducing the ozone dose. In conclusion the implementation of either air or ozone in conjunction of Nanobubble technology delivered excellent results in removing iron and manganese and producing water with an excellent flavour and aesthetic profile.
BREAKWAVE -OZONE NANO BUBBLES
|I.619||Total Dissolved Solids||mg/l||250||260|
|5.308||Manganese as Mn||mg/l||0.013||0.001|
|5.308||Iron as Fe||mg/l||0.0052||0.036|
Figure 1 FINAL RESULTS OF FILTRATE
Manganese and Iron present in water, low pH and low levels of bromide.
Iron levels were up to 3 ppm , manganese up to 1 ppm and the water was slightly acidic at a pH of 6.5.
Ozone oxidation of the dissolved metals using innovative Nano bubble technology. This was followed by precipitation in a conical tank, aeration and filtration in twin catalytic media filters. The additional venturi air injection also displaces any dissolved carbon dioxide, therefore increasing the pH. A final stage 1 micron sediment filter was the final step before the water was pumped to the four 30 kL tanks. A recirculating ultraviolet disinfection ensured that water was constantly recirculated and returned to the tanks eliminating any stagnant zones and possible microbial contamination.
The twin media filters are fitted with Clack automated backwash valves that trap the sediment and at pre-set intervals execute an automated backwash and rinse cycle.
The Process at a Glance:
Water is pumped from two bores to a conical tank at a total flow rate of 120 lpm. A sidestream of this flow is treated with ozone employing innovative new nanobubble technology. Ozone is the strongest, fastest, commercially available disinfectant and oxidant for water treatment.
Ozone oxidation reactions take place several thousand times faster than those of chlorine for destruction of bacteria, viruses, yeast, moulds, cysts, mildew, and most other organic and inorganic contaminants. It is also much faster in oxidising metals the like of iron and manganese allowing the formed metal oxides to precipitate out of solution within seconds. The ozone is generated using a compact packaged ozone generator that includes a non-oil lubricated compressor, oxygen concentrator and corona discharge ozone generator. In order to optimise ozone dissolution into the water, Nano bubble technology is employed.
Other technologies do add ozone and oxygen to the water but most of it will be lost to the atmosphere when it rises through the water column to the surface. Nano Bubbles on the other hand Do Not rise; they actually stay suspended or even sink in the water column.The Nano bubble is unique in that it is not very buoyant. The bubble surface takes on a negative ion charge further raising the surface pressure at the liquid gas interface. This phenomenon causes the bubble to sink and will help transfer ozone and oxygen to depth as it slowly diffuses.
The ozonated side stream is pumped into the conical tank where the precipitated metals are collected at the bottom of the sump of the tank. The injected gases have the added benefit of increasing the pH by displacing Carbon Dioxide out of solution. The amount of ozone needs to be optimised to ensure that manganese is not oxidised to soluble permanganate.
The filling of the conical tank, ozone injection and Nano bubbler start-up is fully automated to ensure that the conical tank is always full. Water is pumped from the conical tank to the twin iron removal filters. A secondary air injection loop is used to ensure sufficient oxygen is available to allow regeneration of the catalytic manganese dioxide media in the two filters. Any residual iron or manganese is trapped in the media bed to deliver the high quality water to the four stainless steel storage tanks. A recirculating ultraviolet disinfection loop ensures periodic disinfection of any stagnant zones in the header piping as well within the 4 tanks.
About The Backwash Filters.
The twin backwash filters – two 21” filters vessels contain a proprietary Manganese Dioxide media – MediaPlus . This media only requires air to remain active and primed. Provided there is sufficient backwash flow rate the filters is backwashed on a daily basis. The entire backwash and rinse cycle is fully automated facilitated by a Clack WS1.5” valve. The Clack backwash valves also have diagnostic features and include No Raw Water By Pass motorised valves to ensure no unfiltered water is by-passed during filtration.
The backwash water is pumped into a drainage pipe and pit . The drainage pit contains gravel and Geotextlies allowing for evaporation of the water and facilitating the removal of the sludge.
The Tank Farm:
Figure 8 Select Water Tanks (316 SS)