Design of MICRODYN AQUADYN® UA860 Modules
11 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
4
Design of MICRODYN AQUADYN
®
UA860 Modules
Pre-Treatment of the Raw Water
4.1
The selection of appropriate pre-treatment processes is essential for the efficient operation of
MICRODYN AQUADYN
®
UA860 membrane modules. For UF the pre-treatment processes are
especially important as certain materials may exacerbate the fouling processes or even cause
immediate damage to the membrane module.
Specific site parameters, such as water characteristics and variation of flow distribution deter-
mine the type and amount of pre-treatment necessary for successful operation of the UF sys-
tem. The complexity associated with additional pre-treatment must be weighed against the ad-
vantages and disadvantages of the downstream processes, especially to minimize membrane
fouling and maximize membrane lifetime.
Typical pre-treatment processes include:
Fat, oil and grease removal
Pre-screening
Coagulation and flocculation
Flow (load) equalization
Fat, Oil and Grease Removal
MICRODYN AQUADYN
®
UA860 membrane modules do tolerate a maximum concentration of 5
mg/l emulsified fat, oil and grease (FOG), but no free FOG. If the FOG concentration exceeds
this maximum concentration in the feed water, an additional pre-treatment step has to be in-
stalled upstream the UF system. Generally, FOG is removed by flotation or skimming. The type
of flotation can vary based on local availability and the FOG concentration in the raw feed wa-
ter.
Pre-Screening
All UF plants will require basic pre-screening, to avoid larger particles from entering the mem-
brane module. The TSS load is stated in the technical data sheet (chapter 7.2). Please confirm
the type and sizing of pre-screening equipment with your MICRODYN-NADIR representative.
Depending on the total plant flow rate and the particle size, several types of pre-filtration are
possible; amongst the most common ones for basic pre-screening are auto self-cleaning filters
with 80 to 400
μm openings
, depending on application and water source. For seawater applica-
tions we recommend 80 to 100
μm
screen size for other applications 200 to 400
μm
is suffi-
cient.
A protective in-line UF feed strainer could be omitted in case the pre-treatment process up-
stream of the UF system comprises a final filtering/straining step of particles bigger than
400 µm. With regards of the strainer construction, the use of any material which could lead to
membrane damage in case of strainer disintegration (e.g. stainless steel wire mesh material)
must be avoided. The use of bag filters or “wedge wire” type strainers (or similar), drum filters
or disc filters is advised.
In the event the customer decides not to install a UF feed strainer, it should be realized that
MICRODYN-NADIR cannot be held responsible for any membrane and/or consequential dam-
age caused by the entrance of external harmful material.
Design of MICRODYN AQUADYN® UA860 Modules
12 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
Coagulation and Flocculation
Coagulation and Flocculation are two methods of pre-treatment, in which chemicals are added
to the raw feed water in order to remove specific particles/ foulants that may have a detrimental
effect to the modules located downstream.
Coagulation occurs when a chemical (c
oagulant) is added to water to ‘destabilize’
colloidal
suspensions. In a colloidal suspension, particles will settle very slowly or not at all because the
particles carry electrical charges on the surface that mutually repel each other. A coagulant
(typically a metallic salt) with the opposite charge is added to the water to overcome the repul-
sive charge and "destabilize" the suspension and allow the colloidal particles to stick together
and form flocs.
Conversely, flocculation uses polymers to clump the small destabilized particles together into
larger flocs, which can be separated from the water easily. Flocculation is a physical process
and does not involve neutralization.
Please take note that any carry over of polymer based flocculants/coagulants, especially the
cationic type, are not compatible with MICRODYN AQUADYN
®
UA860 membrane modules. It
is the customer responsibility to ensure that there is no carry over of those polymer based floc-
culants/coagulants into the UF plant which may cause severe and potentially irreversible fouling
of the membrane modules.
Both methods are often used together to allow for largest possible flocs that can easily be re-
moved by either filtration or sedimentation. Alternatively, it is possible to dose coagulant, alu-
minum or ferric based salts, into the UF feed flow, however this is only allowed after discussion
and agreement of MICRODYN-NADIR. Chapter 4.2 - Membrane Fiber and Membrane Module
Specification
Membrane Fiber and Membrane Module Specification
4.2
Detailed information about MICRODYN AQUADYN
®
UA860 membrane modules can be found
on the data sheet. MICRODYN AQUADYN
®
UA860 modules consists of Polyacrylonitrile (PAN)
hollow fiber membranes. The hydrophilic modified PAN material is very well known and widely
used in many applications because of its narrow pore size distribution with high selectivity and
flux.
The UF fibers developed by MICRODYN-NADIR are assembled into a membrane cartridge.
The cartridge filled with the hollow fiber membranes is the MICRODYN AQUADYN
®
UA860
module.
The membrane modules are designed to be installed and used vertically and should not be in-
stalled and used otherwise, this will ensure the correct operation as designed.
The membrane modules are also optimized for low pressure use, which means at lower OPEX
for the whole membrane filtration system.
There are connections on each membrane module of which 2 connections are on the bottom
cap and 2 connections on the top cap. The feed water enters during filtration at the top of the
membrane module. The air feed is located at the top side as well and is used for the air scour-
ing during the hydraulic cleaning cycle. The permeate ports are located on the bottom cap, one
at the side and one in the middle at the bottom of the end cap, which provide treated water flow
during filtration. The two options of permeate connections at the bottom cap provides flexibility
in the design and installation of the membrane modules on the UF rack.
The second opening at the side of the module is required during manufacturing and is not used
in operation.