Design of the Filtration Stage
13 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
Figure 6: Membrane module dimensions
5
Design of the Filtration Stage
Operational specifications are detailed in MICRODYN AQUADYN
®
UA860 data sheet (Ap-
pendix)
The most important aspect of the UF system design is choosing the correct flux rate for a given
water source, application and a specified set of water parameters. If there are temperature fluc-
tuations over the year then the lowest temperature shall be considered when choosing the flux
rate. Subsequently, the required membrane area can be determined based on the chosen flux
rate. The design of the entire system accounts for any disruptions and shut-downs due to
cleaning, disturbances as well as any process impacts from both upstream and downstream
processes e.g. RO system operations and CIP downstream.
In case of industrial water applications, please contact your local MICRODYN-NADIR repre-
sentative, we recommend conducting pilot tests before designing a full scale plant.
A basic P&ID of an MICRODYN AQUADYN
®
UA860 plant is detailed in Appendix
–
Basic P&ID
Auxilliary Equipment
5.1
5.1.1 Tanks
In order to prevent frequent start/stops of the system, the volume of tanks upstream and down-
stream the UF system shall be sized correctly.
Design of the Filtration Stage
14 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
The tanks shall be designed with inlet/outlet valves, drain valves, open overflow pipe and level
switches and level transmitter for the proper liquid level control in the tanks. The level switch
should have the ability to detect high level in order to prevent overfilling and to detect low levels
in order to stop the operation of the system to prevent damage to the equipment (pumps) and
membrane modules. It is recommended to equip the permeate/backwash tank with a level
transmitter for the control system to check if sufficient water is present in the tank to execute
and complete the whole hydraulic cleaning or chemically enhanced backwash (EBF).
The permeate and back flush tank can be designed as a combined tank for easier operation. In
case of a combined tank, the tank must also be sized sufficiently for the above and in addition
minimum one back flush per filtration time, taking into account the lost capacity when the sys-
tem is not operating due to hydraulic cleaning / Chemically Enhanced Back Flush (EBF) as well
as the water loss through hydraulic cleanings and EBF in addition to the buffer capacity men-
tioned above.
The feed and permeate/backwash tanks have to be constructed from non-corroding materials
that will not leach contaminants into the water. The water in the permeate / backwash tank has
to be protected from direct sunlight in order to minimize bacterial and/or algae growth.
Dosing tank(s)
Dosing tanks are required to store the chemicals required to perform the EBF and cleaning-in-
place (CIP). Each frequently used chemical must be stored in an individual dosing tank. It is
recommended for safety reasons that dosing tanks are placed in its individual bund for con-
tainment in case of leaks.
It is recommended to have sufficient storage capacity in the dosing tanks for minimum one
week consumption of chemicals. Please check with the chemical supplier for suitable tanks,
dosing pumps, piping, valves and instrumentation materials compatible with those particular
chemicals.
In case Sodium Hypochlorite (NaOCl) is applied as one of the cleaning chemicals then it is im-
portant to consider that this chemical will lose strength over time and especially at higher envi-
ronment temperature. The degradation rate increases with higher temparture and in direct sun-
light. Hence it is recommended to use a non-translucent tank material and to check the chemi-
cal strength on a frequent basis. Due to off-gassing, the tank must also be designed with vent-
ing of this gas.
It is recommended to store sodium hypochlorite under dark and cool (≤ 15
°C)
conditions.
Cleaning-in-place (CIP) tank
In case intensive cleaning is required, a CIP tank may be required. The cleaning of the mem-
brane modules in CIP mode requires the cleaning of the membrane on the outer surface. In or-
der to cater for the amount of CIP water needed in the membrane module, each tank should be
sized for approx. 70 L per membrane module. Additional allowance would need to be done for
volume of the water in the piping. The tank should also have a freeboard of approx. 20%.
5.1.2 Pumps and Blowers
Feed pump
The feed pump can be designed based on the gross filtration flux; designed head of the pump
can be determined by the amount of pre-pressure upfront of the pump. Allowance for flow and
pressure must also cater for any pre-filtration equipment such as auto-filters up front.
A typical pump to be used can be of a centrifugal design which should be equipped with a fre-
quency invertor for flow control and smooth ramp up and down at each start and end of filtra-
tion.