Graywater treatment technologies and reuse of reclaimed water for toilet flushing

Abstract

The reuse of wastewater is one effective approach to solving the problem of water resource scarcity. However, deterioration in the quality of reused water, such as increased odor and bacterial growth, restricts its reuse. The objectives of this study were to characterize graywater (GW) treatment technology and to verify the suitability of the reclaimed water for toilet flushing. A membrane bioreactor (MBR) and biological aerated filter (BAF) were used to treat GW in a 1-year laboratory-scale experiment. The optimal operational conditions of the MBR and BAF were as follows: hydraulic retention time = 2–3 h, dissolved oxygen = 4–7 mg/L, mixed liquor suspended solids = 3500–4500 mg/L, and contact reaction time = 1.96–5.89 h, dissolved oxygen = 3–5 mg/L, backwash cycle time = 24–48 h, respectively. The MBR treatment resulted in reductions in COD, NH3-N, and turbidity of 60–90%, 80–90%, and 95–99%, respectively, whereas those of BAF treatment were 50–90%, 50–90%, and 80–90%, respectively. The BOD5 values of MBR and BAF effluent were 1.2–4.5 mg/L and 2.5–7 mg/L, respectively. GW treated by both MBR and BAF met the standard for reusing water for toilet flushing. The effluent from MBR, BAF, and BAF + ultrafiltration treatment and purified mixed wastewater was used to simulate toilet flushing at 28 °C, with the addition of 5 mg/L NaClO to the reused water. The residual chlorine levels were 1.5, 0.6, 0.9, and 0.5 mg/L, respectively, after 15 days. No bacteria were detected in any of the reclaimed water after 15 days. The water quality of the effluent of MBR-treated GW was better than that of the mixed wastewater. The results show that it is viable to use GW purified by MBR for toilet flushing. This study provides a scientific basis for the popularization and application of reclaimed water for toilet flushing.

Full text

WATER ENVIRONMENTAL POLLUTION AND STATE OF THE ART TREATMENT
TECHNOLOGIES
Graywater treatment technologies and reuse of reclaimed water
for toilet flushing
Xueli Ren
1
&Yanyan Zhang
1
&Hongbin Chen
1
Received: 25 September 2018 / Accepted: 10 April 2019
#Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
The reuse of wastewater is one effective approach to solving the problem of water resource scarcity. However, deterioration in the
quality of reused water, such as increased odor and bacterial growth, restricts its reuse. The objectives of this study were to
characterize graywater (GW) treatment technology and to verify the suitability of the reclaimed water for toilet flushing. A
membrane bioreactor (MBR) and biological aerated filter (BAF) were used to treat GW in a 1-year laboratory-scale experiment.
The optimal operational conditions of the MBR and BAF were as follows: hydraulic retention time = 2–3 h, dissolved oxygen =
4–7 mg/L, mixed liquor suspended solids = 3500–4500 mg/L, and contact reaction time = 1.96–5.89 h, dissolved oxygen = 3–
5 mg/L, backwash cycle time = 24–48 h, respectively. The MBR treatment resulted in reductions in COD, NH
3
-N, and turbidity
of 60–90%, 80–90%, and 95–99%, respectively, whereas those of BAF treatment were 50–90%, 50–90%, and 80–90%,
respectively. The BOD
5
values of MBR and BAF effluent were 1.2–4.5 mg/L and 2.5–7 mg/L, respectively. GW treated by
both MBR and BAF met the standard for reusing water for toilet flushing. The effluent from MBR, BAF, and BAF + ultrafil-
tration treatment and purified mixed wastewater was used to simulate toilet flushing at 28 °C, with the addition of 5 mg/L NaClO
to the reused water. The residual chlorine levels were 1.5, 0.6, 0.9, and 0.5 mg/L, respectively, after 15 days. No bacteria were
detected in any of the reclaimed water after 15 days. The water quality of the effluent of MBR-treated GW was better than that of
the mixed wastewater. The results show that it is viable to use GW purified by MBR for toilet flushing. This study provides a
scientific basis for the popularization and application of reclaimed water for toilet flushing.
Keywords Graywater .Membrane bioreactor .Biological aerated filter .Toilet flushing .Reclaimed water
Abbreviations
GW Graywater
BW Blackwater
COD Chemical oxygen demand
DO Dissolved oxygen
SS Suspended solids
TN Total nitrogen
TP Total phosphorus
NH
3
-N Ammonia nitrogen
E. coli Escherichia coli
HPC Heterotrophic plate count
T Temperature
HRT Hydraulic retention time
MBR Membrane bioreactor
BAF Biological aerated filter
SBR Sequencing batch reactor
MBBR Moving bed bioreactor
RBC Rotating biological contactor
CW Constructed wetland
PVDF Polyvinylidene fluoride
PLC Programmable logic controller
QYWTP Quyang wastewater treatment plant
BOD
5
5-day biochemical oxygen demand
MLSS Mixed liquor suspended solids
SEPA State environmental protection administration
UF Ultrafiltration
AQSIQ Administration of Quality Supervision, Inspection
and Quarantine
Responsible editor: Angeles Blanco
*Hongbin Chen
bhctxc@tongji.edu.cn
1
State Key Laboratory of Pollution Control and Resource Reuse,
College of Environmental Science and Engineering, Tongji
University, Shanghai 200092, China
https://doi.org/10.1007/s11356-019-05154-6
/ Published online: 18 May 2019
Environmental Science and Pollution Research (2020) 27:34653–34663
Content courtesy of Springer Nature, terms of use apply. Rights reserved.