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Physico-chemical characterization of municipal sewage sludge of a
sewage treatment plant
Deepayan Priyadarshi, Dr Kakoli K. Paul
Department of Civil Engineering, Environmental Engineering Laboratory, National Institute of
Technology, Rourkela, India
Abstract: The management of sewage sludge generated from sewage treatment plant are
supposed to be the challenging job in this century. Their reuse and not dispose to open land is an
eco-friendly attitude. Municipal sewage sludge has been collected from onsite sewage treatment
plant and analyzed for concentration of various metallic species.
Keywords: Sludge; Toxic metals;
1. Introduction:
The growing waste water accumulation is a huge challenge for the world. According to sick
water report (UNEP & UN-Habitat, 2010), up to 90 % of untreated wastewater flows are
generated in densely populated coastal areas, resulting in high pollution of the receiving water
bodies such as river, lake, ground water, ocean. This impacts on living beings and the food chain.
India is the 2nd largest nation with 18 percent of the world’s population according 2011 census
report. This century is facing immense problem of increasing population and hence for the huge
generation wastewater. Rapid urbanization and industrialization increases the demand of water
for irrigation, domestic use and power generation sectors exerting enormous pressure on our
water resources. Utilization of water has been consequently increasing at a fast pace. Disposal of
about 29000 MLD domestic sewage from cities and towns is the biggest source of pollution of
water bodies in India (CPCB, 2006). There are about 269 sewage treatment plants (STP) in India,
of which only 231 are operational, thus, the existing treatment capacity is just 21 percent of the
present sewage generation(CPCB, 2006). The remaining untreated sewage is the major cause of
pollution in rivers and lakes. Treatment of domestic sewage and subsequent utilization of treated
sewage for irrigation can prevent pollution of water bodies, reduce the demand for fresh water in
irrigation sector and hence huge savings in terms of nutritional value of sewage in Irrigation
(CPCB, 2006). Sludge generated from sewage treatment plants need proper disposal and efficient
mode of reuse.
Management of sewage is worse in smaller towns. The sewage is either directly dumped
into rivers or lakes or in open fields (Kamyotra and Bharadwaj, 2011). This dumping option
again pollutes the environment. Approximately 75 to 80 percent of the river’s pollution is the
result of raw sewage, industrial runoff and the garbage thrown into the river (Misra, 2010).
Waste water can be recycled through effective technologies and it can be reused for different
purposes such as agricultural and landscape irrigation, industrial processes, toilet flushing, and
recharge a ground water basin (Misra, 2010). Limit regarding disposal to sewers and inland
surface water are available in Indian standard.
In the present work, we focused on characterization of effluent generated at National
Institute of Technology Rourkela. Quality analysis of the samples were done to check whether it
meets the permissible range.
2. Materials and methods:
2.1 sampling:
Experimental effluent is collected from sewage treatment plant National Institute of Technology
Rourkela, India. Around 2 liters of effluent collected and brought to laboratory for physico-
chemical analysis.
2.2 Sample preparation:
Sample is filtered using whatman filter paper of 125 mm dia.
2.3 Methods of analysis:
The effluent were further analyzed for metal constituents such as Cu, Zn, Ca, Na, Cr, Fe, Ni,
Mg, As, K, Al, Hg, Pb by using Atomic Absorption Spectrometer (PerkinElmer, AAnalyst 200).
Analysis of Arsenic, Mercury is performed using MHS (Mercury Hydride System) as per
guidelines of MHS 15 (PerkinElmer, 2006).
The standard method for determination of pH of sludge has been done (IS: 3025, Part 11, 1983).
This operation is performed with a pH meter (Systronics, pH system 361).The pH meter has an
accuracy of +- 0.02 pH + 1 digit.
Dissolve oxygen concentration of effluent is measured using DO meter (HACH, sension6).
Hardness of effluent sample is determined (IS: 3025, 1983).
Total Solid of effluent is obtained using standard method (IS: 3025, 1984).
3. Result and Discussion:
3.1 Various metal constituent concentration in effluent of National Institute of Technology,
Rourkela have been determined and compared with recommended limit (Rowe and Abdel-Magid,
1995) of constituents in water for irrigation.
Concentration of metallic species present are summarized in Table 2.
•MPC: Maximum permissible concentration
•Maximum permissible concentration of Zn, Cu, Pb, Cr, Ni, As, Hg in sludge is as per
Water Security Agency, Saskatchewan
•Permissible concentration for Na and As in effluent followed Indian Standards: 3307,
1974.
Table. 2
Serial
No.
metal Concentration of
metal in effluent
(mg/liter)
Recommended limits
for metal constituents
for long term
irrigation (mg/liter)
1 Zn untraced 2.0
2 Cu .015 0.2
3 Ca 19.006 -
4 Pb untraced 5.0
5 Cr .336 0.1
6 Fe .618 5
7 Ni .071 0.2
8 Mg 4.294 0.2
9 Al untraced 5
10 As 0.007 0.2
11 Hg untraced -
12 Na 4.715 60
13 K 8.645 0.2
Series 1: Standard value
Series 2: Analyzed value
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Cu Cr Ni As
For Effluent
Series 1 Series 2
Metal like Arsenic, lead, and mercury, and their inorganic compounds, are toxic to human health
as well as environment. These metal concentration are below toxic limit in samples. While
aluminum can be toxic at higher levels. For sample pH 5.9 and soil pH 6.5 to 8.5 it do not have
any adverse effect (Press et al, 2003).
Metal concentration of effluent showing there is no potential danger to ornamental plant, hence
there is no need of releasing water into river as it is usable for plantation. PH, Hardness, Total
solid content, Dissolve Oxygen content are well in limit.
Properties of dried sludge and effluent of Sludge Treatment Plant at National Institute of
Technology, Rourkela.
Table 3.
Zinc: Residential Human Waste, Laundry Graywater, Food Waste are major source of Zn in
waste water (EIP associates, 1999). It comes from corrosion and leaching of plumbing, water-
proofing products. Cosmetics medicines contains Zn. The concentration obtained for Zn in
sludge has no potential danger to be used as fertilizer.
Copper: It comes mainly from corrosion and leaching of plumbing, fungicides (cuprous
chloride), pigments, wood preservatives, larvicides (copper acetoarsenite) and antifouling paints
Serial No. property Unit Effluent On land for
irrigation Indian
Standards: 3307
(1974)
1 pH Unit
less
6.4 5.5-9.0
2 Dissolved
oxygen
Mg/L 1.9 -
3 Hardness Mg/L 335.0 -
4 Dissolved
solid
Mg/L 318.0 2100.0
5 Total residual
Chlorine
ppm 0.0 -
(Thornton et al., 2001). However the sludge and effluent sample are well within permissible
range.
Fe: The toilet and the laundry were the predominant sources within the household. Effluent
discharged from STP has Fe in permissible limit.
Na: all household wastewater streams contributed to the overall load discharged to sewer, but the
bulk of the load was discharged from the laundry. Ca, Mg are also discharged from laundry.
Nickel: It can be found in alloys used in food processing and sanitary installations, in
rechargeable batteries (Ni-Cd), and protective coatings (Thornton et al., 2001).
Lead: Chalk, old paint pigments, ceramic dishes, porcelain, cosmetics are major sources
(Thornton et al., 2001).
Arsenic: Arsenic inputs come from natural background sources and from household products
such as washing products, medicines, garden products, wood preservatives, old paints and
pigments (Thornton et al., 2001).
Zn, Cu, Fe, Na, Pb, Ni, As concentration above permissible range in both sample is very toxic
(Lokeshappa et al., 2012). Results analyzed for all these metal constituent are with in limit. For
chromium concentration of metal is more than permissible range. Cr present in the effluents can
be recovered by electro-deposition using insoluble anodes (Baysal et al., 2013).
Conclusion:
Different metals show the toxicity at different concentrations and can be potentially toxic at
sufficiently high concentrations. However, certain metals exhibit toxic effects even at relatively
low concentrations. Metal toxicity depends on the element, its chemical form and its oxidation
state. However, the mechanisms responsible for toxicity are not studied in this paper. The results
show that the sludge produced at National Institute of Technology, Rourkela sewage treatment
plant is eligible for plantation purpose. Effluent can be applied for watering flower plant and
grassland. However it is in useable range but more study is require for irrigation use to know the
long term effect of effluent on irrigation land. Regular monitoring should be enforced as these
metal accumulation in vegetables and food stuff can be toxic to consumers. But for ornamental
plants this effluent can be used without any harm to plant and public health. Hence there is no
need of disposal of effluent. NIT Rourkela sludge treatment plant is reducing pollution by
treating waste water well and producing effluent of good quality for ornamental plantation.
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