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Special Report 特別企劃 Tech Notes 技術專文 New Visions 新象新知 LOHAS Column 樂活園地
090
Using ‘TransMembrane
ChemiSorption’ (TMCS) for
Ammonia Removal from Industrial
Waste Waters
以中空絲膜取出廢水中的氨氮
3
3
1
1
1
文│Stasiak Ulbricht Schneid Munos² Sengupta² Kitteringham² Wiesler² 李玫 王義信 │
1 2 3 on the water pH as shown in Figure 1.
Membrana GmbH Membrana Charlotte 新廠設計部│
The extraction of ammonia using membrane contactors provides several advantages in solving a common problem in the
wastewater streams of many industries. Some possibilities and limitations of the ammonia removal process will be shown
based on experience gained through pilot studies. These pilot systems provide data that will allow scale up to full-sized
commercial plants under comparable
conditions.
With this separation technique,
ammonia as a gas species is stripped
from an aqueous liquid “feed” phase
and captured into an aqueous liquid
“receiving” phase in the same membrane
device. The membrane used in this
process is a microporous hydrophobic
hollow fiber, with no inherent selectivity
between permeating species. Because
the membrane is hydrophobic it can be
used to separate the feed phase and the
receiving phase; the membrane pores are
essentially gas-fi lled.
This paper presents data from pilot trials
and a full size plant where commercial
membrane contactors are used to remove
and recover ammonia from a wastewater
stream at an industrial site. Actual
waste water from the site containing
high concentrations of ammonia was
introduced on the shell side and a dilute
sulphuric acid solution was introduced
on the lumen side of the hollow fibers
inside of the modules. Prior to entering the membrane system the wastewater was dosed with a sodium hydroxide solution
to raise the pH. Raising the pH increases the partial pressure of free ammonia in the wastewater making it possible to
remove. The gaseous NH3 diffuses from the waste water phase across the micro porous hollow fi ber membrane wall and
reacts with sulphuric acid in the strip solution to form ammonium sulphate.
INTRODUCTION treatment plants. This translates into high penalty fees that
are paid by the company discharging these contaminates
issolved gases like NH3, H2S or NOx in waste into the sewage stream. In many cases a membrane-
water lead to contamination in the sewage system based water treatment system can be justified because of
Dand high treatment costs for municipal waste water a favorable pay back time. Large-scale processing using
NEW FAB TECHNOLOGY JOURNAL
091
conventional treatment processes such PROCESS through the porous wall due to surface
as extraction, stripping or absorption DESCRIPTION tension effect. Because of the very low
can lead to several problems or issues.
Henry constant and high solubility
For example, a stripping column has a mmonium ion (NH4+) in of NH3 compared to other dissolved
gases in water (e.g., CO2 or O2), the
relatively large footprint and is energy
water reacts with hydroxide
intensive due to complete pressure
free ammonia gas will be difficult to
loss of the treated water. In addition, Aion (OH-) according to the remove by applying vacuum or sweep
following Equation 1.
gas-vacuum combination as in typical
a secondary striping unit is needed to
clean up the striping media air before NH + OH ↔ NH 3 (g ) + H 2 O (l ) Eq 1 degassing operations with Membrane
+
−
4
the air is vented to the atmosphere. This reaction is reversible and can be Contactor technology [2]. However, an
acid solution will work very effectively
Such issues may be overcome by using
an alternate solution called Membrane driven forward or backward depending as a means of removing the ammonia
Contactor technology. Membrane gas from waste water. The low-pH
Contactors can remove ammonia from sulphuric acid solution will instantly
waste water and recover it to a usable react with ammonia gas according to
form in a single step. It is therefore an Fig.1. Solubility of Free Ammonai Equation 2 below to form ammonium
Based on pH and Temperature
adequate and desirable solution for sulphate. This will generate and
treating the ammonia waste water maintain the concentration differential
without polluting the air. or driving force for removing ammonia
R e mo va l o f a m mon i a u s i n g from waste water.
hydrophobic hollow fiber membranes NH 3 /NH 4
in Membrane Contactors has been 2NH + H 2 SO ↔ (NH 4 ) SO 4 Eq 2
3
4
2
tested on small pilot systems in the
past. There is currently very limited The process above generates a
data available on large scale field concentrated solution (up to 30%)
installations. Because there is limited pH of ammonia sulphate, which is a
data there is insufficient knowledge fertilizer. This process, also described
about how to design and size full scale At a pH of 11.3 or higher, the as: “TransMembraneChemiSorbtion”
systems. Operating parameters such as equilibrium favors the formation of free (TMCS) [3], is shown schematically
waste water flow rate, pH, temperature, ammonia gas which can be removed on a commercial available hollow fiber
and the ammonia concentration will from a waste water solution across Membrane Contactor Modul as well
significantly impact the ammonia the air filled pores of a microporous as on a single fiber in Figure 2. The
removal characteristics and removal hydrophobic membrane when a proper wastewater flows through shellside of
Fig. 2. TMCS of ammonia using Liqui-Cel® Membrane Contactors
efficiency. Generating additional data driving force is maintained. The small contactor (outside of the membrane),
is therefore an important step towards pore size and the hydrophobic nature while the acid solution (ex. sulphuric
developing and demonstrating this of membrane prevents the liquid phase acid) is circulating on the lumenside.
technology. from entering into the pores or flowing
http://nfjournal/ July 2011