1. RECOVERY OF INDUSTRIAL EFFLUENT: CASE HISTORY
OF MEMBRANE BIOFOULING AND THE SUCCESSFUL
TREATMENT WITH ALTERNATING NON-OXIDISING AND
OXIDISING BIOCIDE
Martha van Schalkwyk, André Maartens, Pam Allison, Philly Mathe,
Ronel Augustyn and Gerhardt Snyman.
Martha van Schalkwyk – Buckman Africa
e-mail msvanschalkwyk@buckman.com Cell: 082 957 6756
André Maartens – Buckman Africa; Pam Allison – Technical Consultant Buckman
Africa; Philly Mathe – Sasol Synfuels; Ronel Augustyn – Sasol Research and
Development; Gerhardt Snyman – Sasol Technology
ABSTRACT
Keywords: Reverse Osmosis, Treatment of Industrial effluent, Biofouling, Non‐oxidising biocides, Oxidising
biocides
Background: Large quantities of raw water can be saved in the industrial sector when blow‐
down water from large cooling systems and industrial effluents are recovered and re‐used using
membrane technology (Peter Hills, Technology & Engineering, p260, 2000). Biofouling in these
membrane plants is practically inevitable and can be directly linked to as much as 56 to 74% of the
costs of membrane operation (Andrianus van Haandel, Jeroen van der Linde, Handbook biological
waste water treatment, p298, 2007)(Piet Lens, Theresa Mahony, Biofilms in medicine, industry and
environmental biotegnology, p610, 2003) . This paper presents an overview of lessons learned on
full‐scale membrane plants, optimisation of biofouling monitoring and the successful alternation
between oxidising and non‐oxidising microbicides.
Case History: Rapid development of biofilm resulted in the need to implement a
chlorination/de‐chlorination disinfection programme, with an alternating non‐oxidising biocide, for a
17ML/day TRO plant at a refinery in South Africa. High sessile bacteria counts, and high total plate
counts of 105
colony forming units (cfu) per ml
of permeate and 10 6
colony forming units (cfu) per ml
of brine were measured. Microbial populations were monitored using Adenosine tri‐Phosphate
(ATP) measurements, heterotrophic plate counts (HPC), population surveys, bacterial identifications
and microbicide kill studies. A key factor that contributed to the excellent results achieved included
the use of alternating oxidising and non‐oxidising biocides with different active ingredients to
broaden the spectrum of control and minimise microbial resistance. In addition, regular CIP’s and
good operational monitoring and control are essential supplements to the anti‐microbial chemicals.
Both alternating biocides were dosed before pre‐treatment, which consists of sand filters. The sand
filters were heavily contaminated with microorganisms. The oxidising biocide dosing, together with
alternating non‐oxidising biocide, were found to be very effective and resulted in reductions in total
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2. plate counts to <10 2
CFU per ml permeate and <10 3
CFU per ml brine. To protect the rest of the
system downstream (Polyamide RO plant) from the oxidising biocide, total and free halogen were
monitored on a continuous basis.
Conclusions: In the case history presented, application of an oxidising biocide with
alternating non‐oxidizing biocide for feed water disinfection has numerous benefits over
chlorination and de‐chlorination alone. The efficiency of these programmes is however linked to an
effective monitoring strategy. Monitoring the efficiency of the disinfection programmes was done by
using adenosine tri‐phosphate measurements, conventional plate counts, and membrane autopsies.
The subsequent results were: improved disinfection of the sand filters and RO membranes;
reduction in the replacement frequency of membranes; reduced CIP costs and reduction of bio‐
fouling on the membranes.
INTRODUCTION
A water treatment plant at a petrochemical refinery re-utilises saline effluent from
open dams (Refer to Figure 1 for a schematic presentation of the plant layout). The
water chemistry is influenced by various processes upstream as well as seasonal
changes. This continuous change in the feed water composition puts enormous
strain on the water treatment plant, influencing the system’s performance and
ultimately the water recovery on a daily basis. Water recoveries were severely
reduced and tubular cellulose acetate membranes showed evidence of biofouling
and algae growth.
Buckman Africa started shock dosing Oxamine®, an oxidising biocide, on a weekly
basis. After six months, this dosing regime was subsequently adjusted to continuous
dosing. In addition to the oxidising biocide, a non-oxidising biocide was slug-dosed to
address the high microbiological demand in the pre-treatment system. Excellent
microbiological control was obtained with total plate counts of between Log1 and
Log2 cfu/ml on permeate as well as brine samples.
3. 11/20/2009
445
m3/h
Pre‐
Treatment
640
m3/h
275
m3/h
Ash Plant
Permeate
Feed
Water
from CAE
11 modular units
960 off TRO modules
STRO 2.5/1.7 AL9(S) 0398
HP pumps, feed flow
control, flow reversal
system, recovery control
system and chemical
cleaning change over
system
Filter section:
Down flow filters
Backwash system
Antiscalantaddition
Biocide shock
facilities
Intermediate
buffering
Heating of water
TRO membrane plant
Figure 1. Petrochemical water treatment system with pre-treatment system and TRO
membrane plant.
The water treatment plant was commissioned in 1995 and has a capacity to treat
14ML saline effluent per day at a 45% designed water recovery.
The pre-treatment system consists of 5 down flow sandfilters and a backwash
system, followed by a feed tank. An anti-scalant is added into the feed tank. 11
modular TRO membrane units consisting of 960 TRO membranes are fed from the
feed tank.
The saline effluent feed stream comprised of a salty low hazard solution with high
concentrations of calcium, sulphates and sodium. Membrane biofouling is the main
cause of product and membrane losses and is measured through loss in productivity,
salt rejection and pressure drop. Membrane biofouling is addressed by means of
continuous biocide dosing, mechanical cleaning (sponge balls) and Cleaning-in-
place procedures (CIP). The predominant microorganisms associated with biofouling
of this system include Pseudomonas spp, yeasts and Desulphovibrio.
SHOCK DOSING PERIOD
In August 2008, Buckman Africa started dosing Oxamine® before the sand filters.
Dosages were calculated based on residuals obtained before and after each system
namely the sand filters, feed water tank and the membrane plant. Adenosine tri-
phosphate (ATP) analysis was conducted on-site to measure the efficiency of the
programme.
4. The oxidant demand of the pre-treatment system for the disinfectant was extremely
high and consumed most of the oxidant residuals, leaving the rest of the system
exposed. Subsequently the dosing point was moved to a point just before the TRO
membrane plant. This situation was also not ideal as the major source and breeding
ground for microorganisms in the sand filters and feed water tank, was not
addressed.
Total aerobic plate counts indicated that shock dosing was effective, but only for very
short periods. Within a day or two, bacterial re-growth would occur and total plate
counts would reach the original counts obtained before dosing.
CONTINUOUS OXIDANT DOSING WITH ALTERNATING NON-OXIDISING
BIOCIDE SHOCK DOSING
After cost and efficiency evaluations, it was decided to change from shock-dosing to
continuous dosing. Initial dosages of Oxamine® were high in order to obtain
sufficient oxidant residual, but as the system bio-fouling was reduced,
microbiological demand decreased, and dosages could be optimised.
The Oxamine® dosing system is monitored continuously and dosage rates are
adjusted in accordance with the residuals (1 ppm), total plate counts and pH of the
system. The alternating non-oxidising biocide is dosed once a week for a five hour
period.
Total plate counts are performed twice a week after each phase of the system to
determine the biocide efficiency and to enable localised problem-solving if
necessary. (Refer to Figure 2, 3 and 4 for a graphic summary of the microbiological
results). TRO membrane swab analysis is performed every three months to
determine if microbiological population shifts have occurred.
5. Figure 2. Total plate counts obtained during continuous dosing program.
As demonstrated in Figure 2, the system’s total plate counts were reduced after
three weeds from Log6 - Log7 to Log2 - Log3, and these counts remained fairly
constant thereafter in spite of seasonal changes or water chemistry differences.
7. PRODUCT DISCUSSION
Oxamine® is dosed using automated dosing equipment on site and is controlled by
an online pH meter. The pH of the reaction depends on the buffer capacity of the
dilution water and the dilution ratio of the products.
Oxamine® is highly effective against most bacteria, algae and fungi and it is a quick
kill biocide (as shown in Photo 1-5). Although it is a weak oxidising agent, the active
ingredient is not readily consumed by organic material and is therefore able to
penetrate biofilms without being consumed by extra-cellular slime.
Photo 1. Pre-exposed bioflim
8. Photo 2. Biofilm exposed to Oxamine® for 15 mintues
Photo 3. Biofilm exposed to Oxamine® for 30 minutes
9. Photo 4. Bioflim exposed to Oxamine® for 60 minutes
Photo 5. Bioflim exposed to Oxamine® for 90 minutes
The non-oxidising biocide used as a supplement to the oxidising biocide, has long
chemical reacting chains that have the ability to penetrate the slimy extracellular
polymeric layer formed by microorganisms, it does not have as fast a killing rate as
the Oxamine®, but has a half -life of 21 days. Due to this particular characteristic, the
product is ideal to shock-dose to prevent microorganisms building up resistance.
10. FEATURES OF OXAMINE®
- Environmentally compatible – Truly Green Chemistry
- Less effected by suspended solids compared to traditional oxidising
chemistries
- Not as susceptible to pH changes as traditional oxidising chemistries
- The active ingredient can be easily measured and quantified
- More cost effective than traditional oxidising technology
The alternating biocides improved the cleanliness of the feed water to the plant and
reduced biofouling, which extended the membrane life and reduced operating costs.
No negative impact on the differential pressures, salt rejection or flux through the
membranes was recorded.
REFERENCES
1. Peter Hills, Technology & Engineering, p.260 (2000)
2. Andrianus van Haandel, Jeroen van der Linde, Handbook biological waste
water treatment, p.298 (2007)
3. Piet Lens, Theresa Mahony, Biofilms in medicine, industry and environmental
biotegnology, p.610 (2003)
