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A Case Study of Sewage Effluents Polluting the Manohara River

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March 15, 2015


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Sewage is one of the potential polluter of water resources, as it contains organic and inorganic constituents that are responsible for water pollution. The present study is an attempt to find out the pollution caused by Sewage effluents on Manohara River. The result show that the concentrations of chemical parameters are increased in the downstream after the river water is mixed with sewage effluents.


Sewage is the liquid conveyed by the sewer which is defined to be a pipe or conduit for carrying out sewage. It contains over 99.9 percent water, but the remaining material has very significant effects. Sewage differs from sludge in that the later includes the liquid household wastes from kitchen, bathrooms and laundries, but excludes faecal matters and urine. Fresh domestic sewage has a slightly soapy or oily odor, is cloudy, and contains recognizable solids, often of considerable size. Sewage contains both organic and inorganic chemicals. The inorganic constituents are present in the carriage water but increase due to water use. The organic constituents include those present in the wastes discharged to the sewers and their degradation products (Steel and McGhee, 1985).

Sewage may be of several types depending upon the mixture of liquid wastes, as:

Sanitary sewage: Also known as domestic sewage, it is that which originates in the sanitary conveniences of a dwelling, business building, factory, or institutions.

Industrial sewage: It is a liquid waste from an industrial process, such as dyeing, brewing, or papermaking.

Storm sewage: It is a liquid flowing in sewers during or following a period of rainfall and resulting there from.

As industrialization rapidly soars, there is an increasing concurrent prevalence of environmental issues and problems. This is especially true in developing countries where there is an economic need to maximize the use of resources. Water pollution of surface and ground waters is largely a problem in the wake of rising population, rapid urbanization and industrialization. The large scale urban growth has increased domestic wastes while the industrial development manifested either in the growth of new industries or in the expansion of the existing established industries has augmented industrial wastes, the discharges of which into lakes or water courses have brought in hazard of water pollution.

Rivers, streams, ponds and lakes receive the heavy load of sewage, industrial effluents and agricultural runoff. Rivers especially in urban areas are serving as the disposal medium of all kinds of wastes. This condition is very severe in case of the rivers, especially in the rapidly urbanizing cities like those in Kathmandu Valley. The quality of water is of vital concern for mankind since it is directly linked with human welfare. It is the matter of history that faecal pollution of drinking water caused water borne diseases which wiped out entire population of cities .At present, the menaced of water borne disease and epidemics still looms large on the horizons of developing countries.

Discharge of untreated or partially treated sewage may so pollute streams that the water is offensively odorous, resulting in nuisances and possibly depreciated property values.

In most of the rivers, the organic load of the river system is a major problem. Most of the organic load is due to the disposal of sewage in the river system.

After water is used in business and households ,it is collected in a sanitary sewer system and sent to the local waste water treatment .But in most of the developing as well as he developed countries ,untreated or raw sewage is directly disposed in the river system. Municipal wastewater is typically over 99.9 percent water(G.M.Master,1998).The characteristics of remaining portion vary somewhat from city to city, with the variation depending primarily on input from industrial facility that mix with the somewhat predictable residential flows.

The main cause of the river pollution in Kathmandu valley is the discharge of excessive untreated sewage into a small river and dumping of solid waste into the river water and on the river bank (HMG/N (1997). Such untreated sewage and industrial effluents are the most visible causes of contamination along the urban section of river basins in Kathmandu valley. The important adverse effects of such river water are loss of aesthetic, recreational and industrial & domestic value of water, spread of water borne diseases, scarcity of safe and clean drinking water, loss of aquatic biodiversity etc.

The water pollution problems in rivers are so serious that the capacity to sustain the aquatic life has already approached to nil at the urban part of Kathmandu. Industrial wastes are not posing so many problems in comparison to the domestic raw sewage; the concentrations of many toxic substances that are originated by industries are well within the acceptable limits (HMG/N 1997). But existing unorganized and unplanned establishment of industries may create danger in future. Non point sources such as pesticides and fertilizers from agricultural fields carry effluents to the river by the rains.

In context of Nepal, water pollution has reached alarming lever. Lack of town planning, concentration of population in certain pockets and lack of pollution control attitude have lead to serious problems of water pollution. Cities are using rivers as a canal of their waste disposal. In addition, untreated sewage is discharged into the rivers. This practice has turned holy rivers like Bagmati and Bishnumati into polluted rivers. Rivers are deeply associated with Nepalese culture. They use rivers for spiritual purposes. They also use river water for cleaning vegetables and some use river water for drinking.

Site Description

Most of the rivers of Nepal not only provide water but also a major focus of religious and cultural life. Bagmati River is one of those rivers of significance in the Kathmandu valley. It has 24 main tributaries. Of which, within the valley receives six main tributaries. Manahara is one of them. A site in Bodhe where sewage was mixed into river water was chosen for the study.

Manahara River has catchment area of about 77 km2 and is of 26 km long. Its average slope is 38”/km. (Karki, B., 1995). The upper part of the Manahara is connected with “Salinadi” which is one of the most famous religious sites. It starts from the confluence of Salinadi and Ghatte Khola at Sankhu and passes through many Village Development Committees (VDC’s) and Municipalities and reaches to Bagmati at Sankhamul Dovan.

The substrate of the river is mainly the sand through out its length however some gravels and boulders are found in the areas of origin of the river. In upper reaches, it passes through agricultural land and also forest at some parts whereas it passes through settlement areas in lower reaches. Its tributaries are Manmatta Khola at Saranchowk, Mahadev Khola at Bramhakhel, Hanumante khola at Imadol and Kodku Khola at Phubari.

Literature Review

There are several Researches done in Nepal on water and river pollution due to sewage.

Jaisee, Narayan Moni (1991) in his dissertation “Study on the effect of some physico-chemical parameters on the production and seasonal distribution of zooplanktons in Dhobighat primary sewage disposal pond no: 2” submitted to central department of zoology T.U found that there was a high degree of positive coefficient (r) between different factors like, temp, alkalinity and oxygen and negative correlation coefficient between transparency and pH with zooplankton.

Upadhyaya and Roy (1982) studied chemical parameters in six rivers and rivulets-Dhobi Khola, Manohara, Nakku Khola, Balkhu Khola, Bisnumati and Bagmati. A wide seasonal variation was noted in water chemistry. The Bagmati and Bishnumati had higher total dissolve solids values, specific conductance, and concentrations of Na+, K+ and Cl-.

ENPHO (1996) analyzed water quality in an interval of every three hours to know peak hour pollution load in Pashupatinath area of Bagmati. The investigation showed the load of pollution was high during 10:00 to 13:00 hrs, indicating the cause being the influx of domestic sewage.

Karmacharya (1990) by the study of assessment in the Bagmati River and its tributaries in the Kathmandu town section concluded that the river was extremely polluted and is out of unable condition. Among the Bagmati stations, Sundarighat was found to be most polluted. Dhobikhola and Bishnumati contributed to a greater extent in polluting the Bagmati River than the Manohara.

Pokharel (2001) studied in the macro invertebrates of Bagmati River and concluded that sewage has significant role in polluting the water resources.


Broad Objective:

To study the physico-chemical parameters of sewage effluents from the point source of water pollution.

Specific Objective:

  • To study the change in physico-chemical characteristics of water of Manohara river at distance downstream from the point of outfall of sewage.
  •  To determine the chemical parameter of sewage effluent.
  • To assess pollution of river caused by discharge of untreated sewage effluents.
  • To study the river condition and process.



Preliminary Survey of Study Area

Topographic map study and Preliminary Surveys were carried out along the bank of the Manohara River on foot to determine sampling locations, sewage discharges. Visual inspection of sewage disposing sources around the river is conducted so as to see and have idea of the extent of water pollution in the river.

Sampling Locations

The Site was fixed on the area of sewage disposal in the River at Balkumari Bridge. The first sample was taken from the upstream river water; second sample was taken from the discharge sewage whereas third sample was taken from the downstream river water.

Sampling Period

This sample was collected on the month of November, 2007, in a sunny day in between 12PM and 1 PM.

Sample Collection and Preservation:

Clean plastic bottles of 2 liters volume were used for the collection of water samples from the experimental sites. Temperature was observed. Dissolved oxygen was fixed in the field.

The water and sewage samples were collected from the above sites during the study period. The sample site description, time and date of collection were written on the sample bottles. It was then brought to the laboratory for the analysis on the same day. The sample remained was preserved in the refrigerator for the next day analysis.

Analytical Procedure of Physico-Chemical parameters by Trivedy and Goel(1986) and APHA(1998) are as follows:

 1. Temperature:

Temperature of surface water was determined by using ordinary thermometer. For the measurement of surface water temperature the mercury bulb of thermometer was dipped in the water for about 2 minutes.

2.  PH:

The PH of any water body indicates the extent of acidity or alkalinity. The PH of water was determined by using PH meter.

3. Conductivity:

Electrical conductivity is the ability of a substance to conduct the electric current. In water, it is the property caused by the presence of various ionic species. The conductivity was measured by using digital conductivity meter. The conductivity meter was first calibrated with standard potassium chloride solution of 0.01 N. The temperature was adjusted at 20 oc. The resistance of this portion was noted down. The cell constant could then be computed by

C= (0.001413) (RKCl) [1-0.0191(t-20)]

Where, RKCl = measured resistance in ohms

T = observed temperature

At first, the instrument was brought into the conductivity mode. Then the electrode was washed and rinsed with distill water and then dipped in the beaker containing the sample water. The conductivity reading was noted down after the reading stabilized at the certain point. The temperature was also noted down.

4. Chloride:

Chloride was determined by Argentometric titration method. It was done by titrating 50ml of the sample water using 2/3 drops of potassium chromate as an indicator with silver nitrate solution of 0.002 N strength. The light yellow color produced by the indicator was converted into brick red or tinge red color at the end point.

The chloride content was calculated as:

Chloride (mg/l)    =     a x N x 1000*35.5



A = volume of standard AgNO3 consumed

N= normality (strength) of AgNO3

V= volume of sample taken

5. Dissolved oxygen (DO):

The dissolved oxygen was determined by standard Winkler’s method. The sample water was filled in the BOD bottle without incorporating any air bubbles into the bottle.The dissolved oxygen was fixed at the field by keeping 2ml each of Manganous Sulphate and alkaline potassium iodide to form the precipitate. The content was shake in 8 shape by inverting the repeatedly. Then it was brought to the laboratory an about 2ml of conc. Sulphuric acid (H2SO4) was added to dissolve the precipitate by shaking the content well.

Then the content of the BOD bottle, usually 50ml was titrated with standard sodium thiosulphate (0.025N) using starch as an indicator. The blue color developed by the indicator disappears at the end point. The DO can then be estimated by using formula,

DO (mg/l) = (volume x N)of titrant x 8 x1000

V2 (V1-V)



V1 = volume of the sample bottle

V2 =volume of the content titrated

V = volume of MnSO4+KI added

N=strength of sodium thiosulphate

6. Biological Oxygen Demand (BOD):

To determine the biological oxygen demand, sample water filled in BOD bottle was incubated in incubator at 200 temperature for 5 days and DO content of that incubated sample was determined by titrimetric (Winkler’s) method. The difference between initial DO and final DO and after 5 days incubation was noted as BOD of the water. The BOD of water sample was calculated as, BOD in mg/l = (DO1– DO5) x Dilution factor

 7. Free carbon dioxide:

Free carbon dioxide was determined by titrating with 0.05 NaOH solution using phenolphthalein indicators. The end point was indicated by the appearance of pink color. It can be calculated as, Free CO2 (mg/l) = (ml x N) of NaOH x 1000 x 44            

                                                Volume of sample taken


 8. Total hardness:

Total hardness of water was determined by titrimetric method. This was done by titrating 50ml of sample containing 1ml of buffer solution PH10 with standard Ethylene Diamine Tetra Acetic acid (EDTA) solution using Erichrome Black-T indicator. Water hardness may be caused by the sum of the concentrations of all the metallic cations other than alkali metals, expressed as equivalent calcium carbonate concentration.


Total hardness (as CaCO3), mg/l = 1000 x V1



V1 = volume in ml of the EDTA solution used in the titration, and

V2 = volume in ml of the sample taken for the test.


9. Calcium:

Many indicators such as, ammonium purpurate, calcon, etc.form a complex with only calcium but not with magnesium at higher pH. As EDTA having a higher affinity towards calcium; the former complex is broken down and a new complex is formed. However, EDTA has a property to combine with both Ca++ and Mg++. Therefore magnesium is highly precipitated as its hydroxides have sufficiently higher pH.

50 ml of sample was taken. If the sample is having higher alkalinity, smaller volumes diluted upto50 ml should be used. 2 ml of NaOH solution was added in the solution and 100-200 mg of mureoxide indicator was added; a pink color developed and titrated against EDTA solution until the pink color changes to purple. For better judgment of end point, the purple color should be compared with the distill water blank titration end point.


Calcium (mg/L) =                     ml EDTA used x 400.8



Ml of sample


10. Magnesium:

Calcium and Magnesium form a complex of wine red color with Erichrome Black T at pH 10. The EDTA has got a stronger affinity for Ca++ and Mg++; the former complex is broken down and new complex of blue color is formed. The value of Mg++ can be obtained by subtracting the values of calcium from the total of Ca++ + Mg++.


The volume of EDTA used was found in Calcium determination. Also found out the volume of EDTA used in hardness (Ca++ + Mg++) determination with same, volume of the sample as taken in the calcium determination.


a) Magnesium (mg/L) =             y-x x 400.8

Volume of sample x 1.648


Where, y= EDTA used in hardness determination

x=EDTA used in the calcium determination for the same volume of the sample.

b) Mg++, mg/L = Total hardness (as mg/l CaCO3) – calcium hardness (as mg/l CaCO3) x 0.244

Where, Calcium hardness (as mg/l CaCO3) = Ca, mg/L x 2.497


11. Total alkalinity:

Total alkalinity of water was determined by titrimetric method. 50 ml of water sample was taken with 2/3 drop of mixed indicator (methyl red + ethylene blue) which produced green color. Then the sample was titrated with standard (0.02N) H2SO4 until the end point when sharp blue color was appeared.


Total alkalinity (mg/l) = a x N x 1000 



a = volume of standard H2SO4 used in the titration

N= normality of H2SO4.

V= volume of sample taken


12. Phosphate:

Phosphate content in the given water sample was determined as Inorganic phosphorus by Colorimetric method. In this method, 50ml of the filtered clear sample was taken in a conical flask. 2ml of Ammonium Molybdate was added to it. 5 drops of SnCl2 solution was added to it. The solution became blue and the reading was taken at 690 nm on the spectrophotometer within 5 to 12 minutes. Same procedure was repeated for the standard solutions of different concentrations and for distilled water. Theconcentration was determined with the help of standard curve obtained by plotting standard values (Appendix-2) against absorbance.


13. Iron:

All the iron is converted into ferrous state by boiling with hydrochloric acid and hydroxylamine. The reduced iron chelates with 1, 10 – phenonthroline at pH 3.2 to 3.3 to form a complex of orange- red color. The intensity of this colour is proportional to the concentration of iron and follows Beer’s law, and therefore, can be determined calorimetrically.


Preparation of standard curve:

Stock Iron solution was prepared by dissolving the calculated amount of Ferrous Ammonium sulphate. Standard Iron solutions ranging from 1 to 4 mg/L of iron were prepared. 50 ml volume from each solution was taken and added 2 ml conc. HCl and 1 ml of hydroxylamine hydrochloric solution. The contents were boiled to half of the volume for dissolution of all the iron. It was cooled and added 10 ml ammonium acetate buffer and 2 ml phenonthroline solution. If the sample contains interference of heavy metals, 10 ml of phenonthroline instead 2 ml should be added. An orange-red colour appeared and made the volume to 100 ml by adding distilled water. The absorbance was recorded i in spectrophotometer after 10 minutes at 510 nm. Then a standard curve of absorbance versus concentration was prepared. Similarly, 50 ml of sample containing not more than 4 mg/L of iron was taken and similar procedure as done in standard curve preparation was followed to develop the orange – red colour. The absorbance was noted in spectrophotometer at 510 nm and its concentration obtained by using the standard curve.




The above tested parameters have their importance in the different aspects. Temperature is basically important for its effect on properties like speeding of chemical reaction, reduction in solubility of gases, amplification of tastes and odors etc. Temperature in the studied sites are 180c in the upstream site, 220c in the sewage and 70cin the downstream site. Sudden increase in temperature in a water body is an indicator of pollution. There is no such sudden increase in the temperature of water body due to sewage, which may be due to ambient conditions or other unknown factors.


Similarly, in aquatic ecosystem, the pH of water is a function of the dissolved CO2 content that in turn is decreased by photosynthesis and increased by respiration. Higher pH value indicates that the water is rich in carbonates, bicarbonates, and associated salts. In the analyzed samples, the pH of water was decreased after the sewage mixing; this may be due to acidic nature of sewage caused due to human excreta.


Chloride ion is one of the major inorganic anion in water and waste water. The chloride content was found to be higher in sewage and it can be due to the presence of sodium chloride, a common article of diet that passes unchanged through digestive system. The sewage has also greatly affected the chloride content of water.


Electrical conductivity is a measure of water’s capacity to convey electric current. Conductivity of water varies directly with the temperature and is proportional to its dissolved mineral matter content. Conductivity of sewage was found to be high. This may be due to dissolve of many minerals to the sewage through domestic uses.


Alkalinity of water is its acid neutralizing capacity. It is the sum of all the testable bases. On other hand, the hardness of water is not a pollution parameter but indicates water quality mainly in terms of Ca++ and Mg++ Calcium is an essential element for man (@ 2g daily) and for plant growth.


The amount of free CO2 depends upon the PH of water. At lower PH, free CO2 is more but at higher pH, the amount of CO2 decreases. Free carbon dioxide is a normal component of natural waters. The present of free CO2 in water is responsible for its corrosive action as it damages calcareous building.


Phosphate occurs in water as inorganic and organically bound phosphates. Phosphates are largely used for laundry purposes, treatment of boiler water and agriculture. The runoff from all these sources finds their way into water bodies.


Likewise, Iron is the major component of almost all natural water resources. But its high concentration may cause different problems like staining of clothes, water tastes metallic etc. It also leads to the corrosion of pipes, pumps etc. and may lead to deposition of Ferric Hydroxide. High value of these parameters in the sewage sample shows the high concentration of human waste and also industrial waste. Also the data reveal that the river characteristics are greatly altered by the presence of sewage.


DO and BOD have inverse relation in showing water quality, in that, water having high DO will have low BOD and suitable to be used.  As the DO in water decreases, BOD of that water increases and vice-versa. The samples show that sewage has high BOD and low DO, showing the anaerobic conditions in the sample, thus favorable for anaerobic bacteria to live on. Already the BOD of river water is high, but it has further been aggravated by the addition of sewage.



Thus this study shows that, sewage has high potentiality of causing pollution of water bodies, causing the water to be unfit for using it.


From the above analysis and observation, it was found that all the parameters studied for sewage have higher value and that makes the downstream more polluted significantly. Since there was a direct discharge of sewage from households, there should be the presence of alkali salts of sodium and potassium in addition to these of calcium and magnesium because the analysis has showed that there is the greater value of alkalinity than that of hardness. Dissolve oxygen in the sewage was found to be very low and higher BOD value that indicates the higher organic pollution in sewage.



  1. Awareness progammes should be conducted to Local people about the importance of water, not to discharge household waste and sewage in the river directly.
  2. Solid waste, waste water and storm water should be managed in an integrated approach.
  3. Sewage should be managed at the source, not direct disposal to river bodies.
  4. Primary treatment facility should be necessary before mixing of sewage to river bodies.
  5. There should be another solution for sewerage collection and disposal.


APHA (1998), Standard methods for the examination of water and wastewater, 20th edition.

DHM, HMG/N (1997). “Water Quality Data of Rivers of Kathmandu Valley”, Department of Hydrology and Meteorology, Hydrology Division, Kathmandu, Nepal.

ENPHO, 1996 “Report on the Water source Monitoring Programme for Shivapuri Watershed by Assessing Water quality, Kathmandu”.Environment and Public Health Organization.”

Goel, P.K. and Trivedy R.K. (1986), Chemical and Biological Methods for water Pollution Studies, Environment Publication, KARAD (India).

Jaisee, N. M. (1991), Study on the effect of some physico-chemical parameters on the production and seasonal distribution of zooplanktons in dhobighat primary sewage disposal pond no: 2, M.Sc. Thesis, Central Department of Zoology, T.U.

Karki, B., 1995 “Water Quality, Distribution and Abundance of Some Benthic Macro- invertebrates in Manahara River”, (M.Sc. Dissertation in zoology in TU).

Karmacharya, A.P. (1990). “Water Pollution Assessment in the Bagmati River and its Tributaries in Kathmandu Town Section”, Central Department of Botany, Tribhuvan University, Kathmandu, Nepal.

Master,G.M(2004)., “Introduction to Environmental Engineering and science”,2nd edition.

Pokharel, L. (2001), Study on Physico-chemical parameters of water and composition of macro invertebrates of Bagmati River, M.Sc. Thesis, Department of Zoology.

Steel, E.W. and McGhee, T.J (1985), Water Supply and Sewerage, Fourth Edition, McGraw-Hill Book Company,

Upadhaya, N.P. and Roy, N.N. (1982), Studies on river pollution in Kathmandu valley. Indian Journal of .Environmental Health, Vol 24 No2:124-135.

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