DHS(Down-flow Hanging Sponge) Bio -Tower a Sustainable Method for
Waste Water Treatment
Rakesh Kumar Bhardwaj*, 1), Hariom Sharma2), and Surender Kumar Bhardwaj3)
1)
Department of Chemistry, Dyal Singh College, Karnal – 132001, INDIA
e-mail: [email protected]
2)
3)
PWD Water Supply & Sanitation, Water Testing Laboratory, Karnal – 132001, INDIA
Department of Bio-Sciences, Maharshi Dayanand University Rohtak – 124001, INDIA
Abstract
Substantial sustainability integrates social, environmental, economic and institutional aspects, and
extends the scope of planning to distant regions and future generations. In spite of unprecedented
advancement in technology, globalization and urbanization across the world, a vast number of
developing countries are lagging behind in providing basic sanitation and adequate water supply to
the people. The present day speedy socio-economic development of humanity has most vigorously
stimulated the change in nature. Technological advancement, if on one hand has bettered the life of
humans on this planet; on the other hand it has sharply intensified the pollution in environment. The
energy and materials needed to sustain the present society are derived primarily from non-renewable
fossil resources, which will be depleted at some point. The treatment of waste water generated as
sewage has become both an ecological as well as an economic necessity. The investigations over the
years have observed that the presence of toxic compound in water has manifested itself in various
types of diseases in human-being and adversely affect the plants growth. Discharge of chemicals from
various industries causes hazardous effects on humans, animals and environmental balances. The
present study summarizes the result of analysis of sewage effluents of Karnal city being drained into
Yamuna river, an important tributary of Ganga (our pious GANGA), in the region of eastern Haryana
(INDIA). The sewage samples were collected at regular intervals and were analysed for TSS, BOD,
COD, ORP and pH. The concentration of toxic metals Pb, Hg, Cd, and As have been determined for
the samples . DHS(Down-flow Hanging Sponge) Bio Tower the combination of anaerobic (UASB)
with aerobic ( DHS) a self-sustainable sewage treatment system shows tremendous decrease in the
value of BOD5 - 97 % (176mg/kg to 5 mg/kg ) and COD - 94% (476 mg/kg to 27mg/kg) in the
sewage samples of Karnal.
Keywords: Waste water, Toxic chemicals, Sustainable methods
*
Corresponding Author
1. Introduction
The increasing scarcity of water in the world along with rapid population increase in urban
areas gives reason for concern and the need for appropriate water management practices. In
the closing decades of the 20th century environmental pollution emerged as a major concern
for the survival and welfare of mankind throughout the world. Modern civilization, armed
with rapidly advancing technology and fast growing economic system is under increasing
threat from its own activities causing water pollution, Singh et al. (1989). India is the seventh
largest country in the world with a total landmass of 3.29 million sq. km, population over 1
billion, 29% of which live in urban areas spread over 5162 towns. With enormous natural
resources and growing economy India is the second largest pool of technical and scientific
personnel in the world. Pollution from small size industries (SSIs) puts the Indian regulators
in front of a difficult arbitrage between economic development and environmental
sustainability. The uncontrolled growth in urban areas has made planning and expansion of
water and sewage systems very difficult and expensive, Looker (1998).
The pollution load is characterized by high colour content, suspended solids, nutrients and
toxic substances such as heavy metals and chlorinated organic compounds. The discharge of
coloured wastewater from textile, leather, printing and other industrial effluents containing
toxic compounds viz. Cd(II), Pb(II) and Cr(VI) is currently a major environmental concern in
the developing countries because of their poor bio-degradability, carcinogenicity and toxicity,
Yadav et al. (1998). Azo-dyes are the most widely used among synthetic dyes, representing
almost 70% of the textile dyestuffs produced, Knackmuss (1996). Storm water runoff and
discharge of sewage into the water bodies are two common ways by which various nutrients
enter the aquatic eco-system, Sudhira et al. (2000); Kansal et al. (2003). The abuse of water
use for diluting human excreta and transporting them out of the settlement is increasingly
questioned and being considered unsustainable, van Lier et al. (1998).
2. Methods and Materials
The same sampling protocol was employed for each measurement. Routine sampling was
employed during dry weather to characterise water quality under ‘normal’ operating
conditions, and opportunistic sampling was undertaken during rainfall. As the physical and
chemical characteristics of sewage vary from top to bottom of the sewage depth as well as
with time from morning to evening so the grab samples were collected at regular interval and
were mixed together. The samples were filtered in the field immediately after sampling and
subsequently collected in clean polyethylene bottles. The water samples were collected from
the selected area of Karnal and Panipat(an industrial town) in a routine manner for 30 weeks
in continuation covering seasons of year 2007-2008. Simultaneously the samples were also
collected from the Down-flow hanging sponge (DHS) reactor Bio-Tower, installed at a
sewage treatment plant Karnal. The pH was measured using the Systonic pH meter-324. The
samples were analysed for the BOD and COD as per the manufactures manuals for
calibrations of the apparatus and operations. For the measurements of BOD, the BOD bottles
of capacity 300 ml and the incubator was provided with a temperature control of ± 0.50 C.
The estimation of suspended solids was carried out by measuring the weight of residue
retained on the glass fiber filter (Whatman Grade 934 AH) in the known volume of the
samples. For toxic metals analysis, samples were collected from Panipat in 100 ml
polyethylene bottles and acidified with 0.5 ml of Conc. HNO3 to pH 2 and few drops of
HgCl2 were also added to stop the microbiological activity. The pre-treated samples were
taken into the polarographic cell with appropriate supporting electrolyte. Currents were
measured at peak potential of concentrated ion after making blank corrections. Dropping
mercury electrode was used as the working electrode. All the mass measurements were
performed on an electronic balance (Citizen). The experiments were carried out at 25 ± 1 0C.
The samples were stored in refrigerator before analysing and the reagents used in the
estimation were of AR grade.
3. Result and Discussion
Sewage is the wastewater released by residence and industries in a community. It consists of
more than 99 % water with only less than 1 % of dissolved and suspended solid material. The
experimental results of our measurements in the samples of sewage for the BOD, COD, ORP
TSS, VSS and pH, are reported in Table 1 and are graphically represented in Figure 1-3.
Quantitation in all observations was made by standard addition method, Willard et al. (1974).
Table 1 : Experimental measured values of pH , BOD, COD, ORP, TSS and VSS
Time
/Week
pH
ORP
(v)
BOD
(mg/kg)
COD
(mg/kg)
Sewage
Sewage
Sewage
UASB
UASB
+ DHS
1
7.19
-281
151
28
2
2
7.12
-278
167
66
3
7.13
-266
169
4
7.05
-278
5
7.21
6
Sewage
TSS
(ppm)
VSS
(ppm)
Sewage
Sewage
UASB
UASB
+ DHS
356
189
33
263
187
5
578
185
27
275
179
70
5
560
140
40
208
118
186
65
6
460
156
40
255
172
-249
144
60
9
385
197
24
180
98
7.16
-258
160
52
1
516
198
32
348
267
7
7.13
-252
172
55
4
420
226
31
158
85
8
7.21
-240
201
58
3
556
186
22
225
157
9
7.21
-215
228
50
6
600
228
30
315
245
10
7.28
-231
214
67
2
533
158
18
185
119
11
7.13
-231
199
52
3
584
178
36
233
171
12
7.14
-251
192
60
7
566
176
27
263
227
13
7.29
-220
180
42
5
496
180
14
225
150
14
7.22
-245
177
54
5
463
190
16
155
105
15
7.30
-152
182
70
6
462
185
25
283
206
16
7.21
-203
172
64
7
481
162
25
194
120
17
7.15
-253
139
53
9
410
160
20
247
157
18
7.18
-248
161
48
6
487
189
42
258
150
19
7.22
-247
134
53
4
411
178
30
220
158
20
7.25
-251
165
50
8
450
196
49
195
130
21
7.17
-257
179
47
10
487
169
36
208
125
22
7.21
-267
193
63
3
579
200
28
170
110
23
7.29
-239
156
72
4
611
211
30
333
250
24
7.10
-211
188
61
8
426
165
28
233
165
25
7.22
-244
178
49
9
407
164
31
247
157
26
7.28
-207
161
63
3
335
170
14
153
89
27
7.19
-252
172
43
4
386
168
10
135
97
28
7.21
-261
190
44
6
410
161
16
272
206
29
7.33
-242
169
71
7
380
168
17
215
139
30
7.18
-248
201
48
6
487
189
42
258
150
Table 1 revealed that the composition of wastewater varies significantly with session as a
result of the release of untreated domestic and industrial inorganic and organic toxicants.
Figure 1 shows that the variation of studied parameters over the study period is not regular
but at random, the studied parameter as a whole increases with alarming rate. The BOD5
measures the amount of oxygen microorganisms required in five days to break down sewage.
The amount of BOD varies from 144 mg/kg to 228mg/kg averaged 176.0(mg/kg); while
COD 335 mg/kg to 611 mg/kg averaged 476(mg/kg) and pH 7.05 to 7.33 averaged as 7.20.
The cloudiness of sewage is caused by suspended particles. The TSS ranges from 155 to 348
ppm while the VSS is averaged as 150 ppm.. The ORP (oxidation reduction potential) is a
measure of energy potential. Table 1 indicates the values of ORP various from -152 V to -281
V averaged as -242.5 V An ORP in the negative range indicates reaction taking place is
anaerobic, while the positive value of ORP indicates that the reaction is aerobic or there is
presence of oxygen.
ORP
BOD
COD
TSS
VSS
700
600
500
400
300
200
100
0
-100
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
-200
-300
-400
Figure 1 Variation of BOD , COD, TSS, VSS and ORP in waste water with Time ( in week)
BOD (Sewage)
BOD (UASB)
BOD (UASB+ DHS)
250
200
150
100
50
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Figure 2
Variation of BOD with Time ( in weeks)
COD ( Sewage)
COD ( UASB)
COD (UASB+ DHS)
700
600
500
400
300
200
100
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Figure 3
Variation of COD with Time (in weeks)
Heavy metals from waste-water are partitioned into sewage sludge and the effluent and are
returned to the environment where they may contaminate soil, water and eventually also the
food chain. While some metal compounds are essential to animals and humans, others are
known to be toxic and the environmental impact of many of them has to be elucidated
Many industrial plants discharged heavy metals and volatile organic chemicals (VOCs)
directly into streams or inject them into the subsurface. The chemicals used in the dyeing
factories viz sodium nitrate, aluminum sulphate, caustic soda and soda ash may be
responsible for high value of the studied parameters. Similar results were also reported by
Somashekar et al. (1984). The measured concentration of toxic metals Cr, Pb, As, and Hg in
the sewage samples of Panipat town along with standard deviation have been summarized in
Table 2. It can be seen from the tabulated values that the level of toxic metals in the waste
water is much higher.
Table -2 Concentrations of toxic metal and standard deviation σ in wastewater
Metal ion
Supporting Electrolyte
Peak
Concentration
Potential(v)
(mg/kg)
σ±
Max.
Min.
Avg.
Lead
0.1M KCl
-0.44
139
52
96
1.6
Chromium
1 M NaOH
-0.80
112
69
75
2.6
Mercury
0.5M HCl + 0.5M H2SO4
+0.19
28
11
16
2.4
Arsenic
Oxalate Buffer (pH 4.0)
-1.15
17
6
13
1.2
The main components of domestic wastewater are proteins, carbohydrates, detergents,
tannins, lignin, fulvic acid, and many other dissolved organic compounds, Rebhun et al.
(1971). Pathogens or disease-causing organisms are present in sewage. Coliform bacteria are
used as an indicator of disease-causing organisms, Kansal et al. (2003).
A number of conventional treatment technologies have been considered for treatment of
wastewater contaminated with organic substances. Commercial activated carbon is regarded
as the most effective material for controlling the organic load. However due to its high cost
and about 10-15 % loss during regeneration, unconventional adsorbents like fly ash, peat,
lignite, wood, saw dust etc. have been used for the removal of refractory materials, Pandey et
al. (1985) for varying degree of success. Ionic liquids holds promise to provide better
alternative to the toxic solvents, Sheldon et al. (2001).
The removal of organic material by adsorption has recently become the subject of interest of
several workers, Nelson et al. (1969); Eye et al. (1970); Johnson et al.(1965); Deb et
al.(1966); Gupta et al.(1978,1990); Mott et al. (1992); Viraraghavan et al.(1994). They have
explored the use of fly ash as an adsorbent for treatment of wastewater to remove toxic
compounds and colour. Pandey et al.(1985), has proposed a method for removal of copper
from wastewater by taking fly ash as an adsorbent. The use of active filtration through
alkaline media for the removal of phosphorus from domestic wastewater has been proposed
by Johansson et al.(1998); and Drizo et al. (2006). Ozone is a very good oxidizing agent due
to its high instability (reduction potential 2.07 V) when compared to chlorine (1.36 V) and
H2O2 (1.78V). It has potential to degrade large number of pollutants like phenols, pesticides
and aromatic hydrocarbons and is used since the early 1970s in wastewater treatment
(Robinson et al. 2001, Özbelge et al. 2002, Pera-Titus et al. 2004). The major drawback of
the use of this method is, ozone has short half-life, it decomposes in 20 minutes so require
continuous ozonation and making this method expensive to apply, Slokar et al. 1998,
Robinson et al. 2001).
Anaerobic wastewater treatment is a biological wastewater treatment without the use of air or
elemental oxygen. Applications are directed towards the removal of organic pollutants in
wastewater, slurries and sludge. Complete replacement of aerobic with anaerobic technology
is not yet possible as the effluent quality of anaerobic treatment systems is not up to par. The
anaerobic treatment is considered as a pre-treatment technique and has been applied in
Colombia, Brazil, and India, replacing the more costly activated sludge processes. There are
different types of digesters available, some have been proven effective over time, and others
are still being tested. One of the most suitable digesters for tropical conditions is the UASB
(Up flow Anaerobic Sludge Blanket).
Harada et al. (2007, 2006, 2005, and 2002) has proposed a self-sustainable sewage treatment
system with the combination of UASB as pretreatment unit and an aerobic reactor Downflow Hanging Sponge (DHS) reactor as a post treatment unit shown in Figure 4. The
proposed anaerobic-aerobic biocoenoses of UASB and DHS fulfills the need for a simplified
treatment system for developing countries because of its low cost, and operational simplicity,
along with sustainability of the system as a whole. The results in Table 1 and Figure 2 & 3
show a tremendous decrease of 97 % in BOD5 (176mg/kg to 5 mg/kg ) and 94% in COD
(476 mg/kg to 27mg/kg in the samples collected from DHS Bio Tower reactor at Karnal.
BioGas
Anaerobic
HRT : 6 Hr
UASB - Effluent
Aerobic
HRT : 2 Hr
Gas -Solid
Separator
Polyurethane
Perforated
Plate
Aeration
Sponge
Carrier
Water
Jacket
Sewage Tank
Final
Effluent
Sludge Bed
UASB- Pre Treatment Unit
DHS – Post
treatment Unit
Figure 4 Schematic diagram of anaerobic (UASB) with aerobic (DHS) sewage treatment.
4. Conclusions
An increasing proportion of the human population is concentrated in towns, which is
associated with the production of large volumes of waste-water that must be treated before
discharge in to a recipient.. To achieve ecological wastewater treatment, a closed-loop
treatment system is the need of hour. Now a day’s most of the systems under operation are
“disposal-based linear system”.
These traditional linear treatment systems must be
transformed into the cyclical treatment to promote the conservation of water and nutrient
resources. It can be concluded from this study that combination of anaerobic (UASB) with
aerobic (DHS) a self-sustainable sewage treatment is a good alternative to other conventional
treatment system.
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