Journal of Hazardous Materials 266 (2014) 10–18
Contents lists available at ScienceDirect
Journal of Hazardous Materials
jou rn al hom epage: www.elsevier.com/locate/jhazmat
Effect of coagulation on treatment of municipal wastewater reverse
osmosis concentrate by UVC/H
2
O
2
Muhammad Umar, Felicity Roddick
∗
, Linhua Fan
School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne, 3001 Victoria, Australia
h i g h l i g h t s
•
Alum coagulation is an effective pre-treatment for UVC/H
2
O
2
treatment of high salinity ROC.
•
Comparable DOC in samples but different coagulation success due to different nature of organics.
•
Comparable mineralization obtained for two different ROCs with UVC/H
2
O
2
only treatment.
•
UVC/H
2
O
2
treatment led to increased biodegradability with and without coagulation.
•
Significant reduction in energy consumption obtained after pre- and biological post-treatment.
a r t i c l e i n f o
Article history:
Received 16 August 2013
Received in revised form
24 November 2013
Accepted 5 December 2013
Available online 12 December 2013
Keywords:
Coagulation
Alum
UVC/H2O2
Reverse osmosis concentrate
Biodegradability
a b s t r a c t
Disposal of reverse osmosis concentrate (ROC) is a growing concern due to potential health and ecolog-
ical risks. Alum coagulation was investigated as pre-treatment for the UVC/H
2
O
2
treatment of two high
salinity ROC samples (ROC A and B) of comparable organic and inorganic content. Coagulation removed
a greater fraction of the organic content for ROC B (29%) than ROC A (16%) which correlated well with the
reductions of colour and A
254
. Although the total reductions after 60 min UVC/H
2
O
2
treatment with and
without coagulation were comparable, large differences in the trends of reduction were observed which
were attributed to the different nature of the organic content (humic-like) of the samples as indicated by
the LC-OCD analyses and different initial (5% and 16%) biodegradability. Coagulation and UVC/H
2
O
2
treat-
ment preferentially removed humic-like compounds which resulted in low reaction rates after UVC/H
2
O
2
treatment of the coagulated samples. The improvement in biodegradability was greater (2–3-fold) dur-
ing UVC/H
2
O
2
treatment of the pre-treated samples than without pre-treatment. The target DOC residual
(≤15 mg/L) was obtained after 30 and 20 min irradiation of pre-treated ROC A and ROC B with downstream
biological treatment, corresponding to reductions of 55% and 62%, respectively.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Increasing use of reverse osmosis (RO)-based processes in water
and wastewater treatment has led to significant attention being
paid to the treatment of the resultant RO concentrate (ROC). The
successful rejection of various inorganic and organic contaminants
by RO membranes results in their elevated (3–4-fold) concentra-
tions in ROC. The addition of chemicals (antiscalants, biocides and
acids) further complicates the situation as they can change the char-
acter of the organic and inorganic pollutants and can influence the
chemical equilibrium of the dissolved constituents [1]. The geno-
toxicity of a ROC was investigated in a recent study by Tang et al. [2]
using the SOS umu method and found that it ranged between 500
and 559 g 4-NQO (4-nitroquinoline-1-oxide)/L, which was much
∗
Corresponding author. Tel.: +61 3 9925 2080; fax: +61 3 9639 0138.
E-mail address: felicity.roddick@rmit.edu.au (F. Roddick).
higher than for the RO influent (105–160 g 4-NQO/L). Therefore,
discharging the ROC to the environment can pose serious toxicolog-
ical and environmental risks. Some facilities have made treatment
of ROC mandatory prior to its discharge. For example, in Brisbane
(Australia), the Bundamba advanced wastewater treatment plant
which contributes purified recycled water to the Western Corri-
dor Recycled Water Scheme, the largest recycled water scheme in
Australia and the third largest advanced water treatment project
in the world, is required to treat ROC and monitor nutrients and
metal concentration prior to its discharge to the Brisbane river [3].
In addition to minimizing the environmental impacts, economi-
cally profitable reuse applications can help to offset the costs of
treatment processes [4].
Due to the successful application of UVC/H
2
O
2
process in drink-
ing water treatment and wastewater polishing after advanced
treatment (e.g., RO permeate), its use in the treatment of ROC has
recently been investigated [5–7]. The process has been reported
to reduce the concentration of organic matter as well as improve
0304-3894/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jhazmat.2013.12.005