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Bioorganic & Organic Chemistry

Research Article Volume 1 Issue 2

Physicochemical characterization of the sewage sludge from guarchia wastewater treatment plant in benghazi-libya evaluation of the organic composition

Khalid M Darwish, Nuha A Naas, Abd Alsalam H Azzouz

Chemistry Department, University of Benghazi, Libya

Correspondence: Khalid M Darwish, Chemistry Department, Science Faculty, University of Benghazi, Benghazi, Libya

Received: April 24, 2017 | Published: May 26, 2017

Citation: Azzouz AAH, Naas NA, Darwish KM. Physicochemical characterization of the sewage sludge from guarchia wastewater treatment plant in benghazilibya evaluation of the organic composition. MOJ Biorg Org Chem. 2017;1(2):30-48. DOI: 10.15406/mojboc.2017.01.00009

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Abstract

Raw sewage sludge collected from sixteen wastewater-pumping stations at Benghazi city and from Guarchia wastewater treatment plant have undergone physicochemical characterizations including pH, total volatile solid (TVS), total nitrogen (TN), total phosphorus (TP), total organic matter (TOM) and total organic carbon (TOC). The monthly and spatial variations in sludge properties have also been described.

Keywords: physicochemical characterization, guarchia wastewater treatment plant, organic composition

Introduction

Until the late 19th century, there have been much concern with the effective and safe disposal of the mankind liquid and solid wastes. The installation of sewerage systems for piping liquid wastes away from major population centers was the single greatest contributor to the dramatic reductions in infectious diseases which occurred during that time. The liquid wastes were usually discharged untreated to a river or the ocean but, with the increasing world population, improved sanitary systems and the adventure of more stringent standards on wastewater treatment, this option has become increasingly untenable.1-2

The processes applied to the treatment of sewage result in the separation of sewage into two streams, a clarified water containing 20-30 mg/l of suspended solids and a sludge stream of 1-3% solids dry weight, which contains 80-90% of nutrients and pollutants present in the raw sewage.1 The nature of the sewage sludge varies, depending on both the wastewater composition (mainly organic and inorganic materials, plant nutrients, trace elements, organic chemicals and some pathogens) and on the treatment processes used.3 Recent studies involved qualitative and quantitative evaluation of wastewater,9 the degradation kinetics of sewage sludge.8 the reuse application of wastewater.10,11 the study of Chemical and Microbial Composition of Municipal Sewage water, the Hydrogen and Methane Production from Biowaste and Sewage Sludge and finally the study of the impact of sewage treatment plant on local environment.12-14 Our current research paper deals with the investigation of the total organic composition of the raw sewage sludge samples collected from sixteen wastewater pumping stations at Benghazi city and from Guarchia wastewater treatment plant to evaluate pH, The total nitrogen (TN), the total phosphorus (TP), The total organic matter (TOM) and the total organic carbon (TOC).

Aim of the work

Wastewater generated by Benghazi is generally pumped to Guarchia treatment plant for treatment. Only one quarter of the pumped quantity of this wastewater can be accepted and partially treated by Guarchia treatment plant, due to its limited capacity and low efficiency, producing unstabilized sewage sludge; which will be disposed-off in open fields, and partially treated effluent, which together with the remained untreated waste-water will be discharged into stream at the Mediterranean Sea in front of the city; the discarded materials contain potential toxic constituents, particularly heavy metals and organic compounds. So far, no efforts to purify water have been conducted in the region. Efficient waste management practices that include potential hazard minimization, recovery operations and treatment prior to stream emission should be implemented. The lack of suitable waste treatment results in discharge of untreated or inadequately treated municipal and industrial sewage into aquatic environment, leading to deleterious health effects. So far, no controls on emissions of pollutants to the environment have been set in the city, although the country established laws and regulations related to water sources conservation since 1973.

Concerning the health and environmental effects of organic chemicals in sewage sludge, the exposure to organic pollutants; for example through drinking water, is very low. However, as some of these compounds may be bio-accumulated or have effects at low concentrations, chronic health effects are starting to be investigated for some of these compounds. In the current research work, the main objectives of the study are:

  1. Determination of some physicochemical properties of sludge such as pH, percent of water content, total volatile solid, total nitrogen, total phosphorus, total organic matter and total organic carbon.
  2. To describe the monthly and the spatial variations of sludge properties.
  3. To find-out the relationships between sludge properties.

Benghazi city contains about 36 wastewater-pumping stations out of which only sixteen pumping stations and Guarchia treatment plant were chosen as sampling points for our research. A monthly sample was collected from every station during the period of Jan-Mar. (2006) and another monthly sample was collected from Guarchia plant during the period of Dec. 2005 -Jan. 2006. For determining the total organic composition, each dried sample was ground with glass pestle and mortar then passed through a 2mm mesh stainless steel sieve. The dried ground samples were then stored in plastic bags into a refrigerator for analysis.4 The required temperature for TN, OM and TP determination was 50 0C. The pH, TS and TVS for each sludge sample were measured directly after sample collection with no need for drying.5

Total solid content (TS)

The water content is a measurement of sediment moisture expressed as a percentage of the whole sediment weight. The sediment moisture content equals the difference between wet weight of the sediment and dry weight following oven drying at 50-105 0C to a constant weight.6

TS(as%of wet sludge)= wt' wt (100) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKqzGeGaamivai aadofacaGGOaGaaiyyaiaacohacaGGLaGaai4BaiaacAgaqaaaaaaa aaWdbiaacckapaGaai4DaiaacwgacaGG0bWdbiaacckapaGaai4Cai aacYgacaGG1bGaaiizaiaacEgacaGGLbGaaiykaiabg2da9Kqbaoaa laaabaqcLbsacaWG3bGaamiDaiaacEcaaKqbagaajugibiaadEhaca WG0baaaiaacIcacaaIXaGaaGimaiaaicdacaGGPaaaaa@5461@
Where wt' is weight of sample after drying; wt is weight of sample before drying.

Total volatile solids (TVS)

This represents the fraction of total solids lost up on ignition at a temperature of 550±100C for 1 h.6
Where wt' is weight lost during ignition; wt is weight remaining after drying.

Volatile matteer (as % of dried solids) =  wt' wt  (100) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKqbakaadAfaca WGVbGaamiBaiaadggacaWG0bGaamyAaiaadYgacaWGLbaeaaaaaaaa a8qacaGGGcWdaiaad2gacaWGHbGaamiDaiaadshacaWGLbGaamyzai aadkhapeGaaiiOa8aacaGGOaGaamyyaiaadohapeGaaiiOa8aacaGG LaWdbiaacckapaGaam4BaiaadAgapeGaaiiOa8aacaWGKbGaamOCai aadMgacaWGLbGaamiza8qacaGGGcWdaiaadohacaWGVbGaamiBaiaa dMgacaWGKbGaam4CaiaacMcapeGaaiiOa8aacqGH9aqppeGaaiiOa8 aadaWcaaqaaiaadEhacaWG0bGaai4jaaqaaiaadEhacaWG0baaa8qa caGGGcWdaiaacIcacaaIXaGaaGimaiaaicdacaGGPaaaaa@6920@
where wt' is weight lost during ignition; wt is weight remaining after drying.

Organic matter and organic carbon in dried sewage sludge (OM % & OC %)

This involves reduction of K2Cr2O7 by OC-compounds followed by determination of unreduced dichromate by redox titration by ferrous ammonium sulfate. The actual measurement is of oxidizable OC but the data are converted to percentage OM using a constant factor, assuming that OM contains 58 % of OC. However, since this proportion is not constant, the results are multiplied by 1.334 as OC.4

N= 10 V blank MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKqbakaad6eacq GH9aqpdaWcaaqaaiaaigdacaaIWaaabaGaamOvamaaBaaajuaibaGa amOyaiaadYgacaWGHbGaamOBaiaadUgaaKqbagqaaaaaaaa@4030@
Percentage OM in sludge:

% Total OC ( w w ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKqbaoaabmaaba WaaSaaaeaacaWG3baabaGaam4DaaaaaiaawIcacaGLPaaaaaa@3A0A@  1.334 x % Oxidizable OC
% OM (w/w) = 1.724 × % Total OC
Where N = Normality of ferrous ammonium sulfate (~ 0.5 M)
10 = Volume of (1 N) K2Cr2O7 solution
Vblank = Volume of ferrous ammonium sulfate solution required to titrate the blank (in ml)
Vsample = Volume of ferrous ammonium sulfate solution required to titrate the sample (in ml)
wt = weight of dried sludge (g)
0.3 = 3 × 10-3 × 100; where 3 is the equivalent weight of C.

Total nitrogen (TN %) in dried sludge

Applying Kjeldahl semi micro methods, using 50 ml Kjeldahl digestion flask, for TN analysis of sediments, the sample must be more finely ground and thoroughly mixed than for the macro-Kjeldahl analysis to minimize sample error.7 The method involves digestion of sample to convert organic-N to inorganic-N as (NH4+ - N) then determination of TN in the digest as (NH4+ - N). The digestion involves heating the sample with H2SO4-containing substances that promote oxidation of OM and conversion of organic-N to inorganic-N (NH4+ - N), being salts such as K2SO4 or Na2SO4, which increase the temperature of digestion, and catalysts such as Hg, Cu, or Se, which increase the rate of oxidation. The (NH4+ - N) is determined by collecting the NH3 liberated by distillation with alkali and analyzing the distillate by titrimetric procedure.7
wt'= v x 0.14 1 ( 100 ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsacaWG3b GaamiDaiaacEcacqGH9aqpjuaGdaWcaaGcbaqcLbsacaWG2baeaaaa aaaaa8qacaGGGcGaamiEaiaacckapaGaaGimaiaac6cacaaIXaGaaG inaaGcbaqcLbsacaaIXaaaaKqbaoaabmaabaGaaGymaiaaicdacaaI WaaacaGLOaGaayzkaaaaaa@4850@
Where wt' is weight of TN (NH4+ - N) in sample; wt is weight of sample; V is volume of H2SO4 required for titration and %N is percentage of TN in sample.

Total phosphorus in dried sludge

The molybdophosphate complex is formed in H2SO4 matrix and reduced with ascorbic acid and absorbance is measured at 840-880 nm. The color is stable from 10 min to 24 h after formation.4 The sample (0.3-0.5 g) in an uncovered crucible was ignited in a muffle at 550 0C for 2 h. After cooling in desiccator, the sample was transferred to a 100-ml calibrated flask, where 50 ml of HCl (1 N) was added.

The mixture was filtered after shaking overnight for 14-18 h at 25 0C. A solution of ascorbic acid in ammonium molybdate (8 ml) was added to the filtrate. Absorbance of the solution was measured at λmax using 1 cm cuvette. A standard curve was prepared by analyzing aliquots of a KH2PO4 solution.

Conc. of ( P ) = ( Abs ×  F 1 × D ) wt MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKqbacbaaaaaaa aapeGaam4qaiaad+gacaWGUbGaam4yaiaac6cacaqGGaGaam4Baiaa dAgacaqGGaWdamaabmaabaWdbiaadcfaa8aacaGLOaGaayzkaaWdbi aabccacqGH9aqpdaWcaaqaa8aadaqadaqaa8qacaWGbbGaamOyaiaa dohacaqGGaGaey41aqRaaeiiaiaadAeapaWaaSbaaeaapeGaaGymaa Wdaeqaa8qacqGHxdaTcaqGGaGaamiraaWdaiaawIcacaGLPaaaa8qa baGaam4Daiaadshaaaaaaa@5182@
Where Abs = absorbance of sample solution; F1 = factor of standard curve (x/y); D = Dilution factor; wt = weight of sample after ignition.

Results and discussion

In station 1, the pH values ranged between 6.16 in February and 6.68 in January (generally acidic). The organic matter concentration was in the range of (21.74-27.23 %), the maximum content was recorded in March and minimum was in February. The lowest content of TN was determined in March (1.52 %) and the highest content was determined in January (2.75 %). At the same time, the lowest value of TP was recorded in March (1.78 %) and the highest value was recorded in February (2.95 %). The C/N ratios were ranging from 3.63 in January to 10.36 in March, due to the changes of OC % contents during the study period (Table 1) (Figure 1).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.68

6.16

6.48

6.16

6.68

---

0.262

OM%

23.67

21.74

27.23

21.74

27.23

24.21

2.785

OC%

13.73

12.6

15.76

12.60

15.76

14.03

1.601

TN%

2.75

1.69

1.52

1.52

2.75

1.98

0.666

C/N

3.63

7.45

10.36

3.63

10.36

7.14

3.375

TP%

2.07

2.97

1.78

1.78

2.97

2.27

0.620

Table 1 Monthly Variations in the Sludge Properties at Station

Figure 1 The C/N ratios were ranging from 3.63 in January to 10.36 in March.

In station 2, the pH values ranged between 6.21 and 6.73 (acidic range). The maximum record of OM was obtained in March (47.81 %) and the minimum was found in January (44.39 %). the contents of TN % were ranging from 3.78 to 4.20 %. The contents of TP % at this station were ranging between 1.35 % in January and 1.93 % in March. Records of C/N ratio were ranging from 6.34 in January to 7.16 in February (Table 2) (Figure 2).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.73

6.36

6.21

6.21

6.73

---

0.267

OM%

44.39

46.72

47.81

44.39

47.81

46.30

1.747

OC%

25.74

27.09

27.68

25.74

27.68

26.83

0.994

TN%

4.06

3.78

4.20

3.78

4.20

4.01

0.213

C/N

6.34

7.16

6.59

6.34

7.16

6.69

0.420

TP%

1.35

1.74

1.93

1.35

1.93

1.67

0.295

Table 2 Monthly Variations in the Sludge Properties at Station 2

Figure 2 C/N ratio were ranging from 6.34 in January to 7.16.

The pH values ranged between 6.82 (acidic) in February and 7.39 in January (neutral). The OM concentration was in the range of 30.44% (March)–37.43 % (January). The contents of TN were ranging from 1.91% to 3.95 % and the contents of TP were ranged between 1.04% (March) and 1.71 % (February). Records of C/N were ranging from 4.64 in March to 10.84 in February; this wide range is due to the difference of OC % contents (Table 3) (Figure 3).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.39

6.82

6.99

6.82

7.39

---

0.292

OM%

37.43

35.79

30.44

30.44

37.43

34.55

3.655

OC%

21.71

20.72

17.55

17.55

21.71

19.99

2.173

TN%

2.08

1.91

3.95

1.91

3.95

2.64

1.131

C/N

10.43

10.84

4.46

4.46

10.84

8.57

3.591

TP%

1.21

1.71

1.04

1.04

1.71

1.32

0.348

Table 3 Monthly Variations in the Sludge Properties at Station 3

Figure 3 Records of C/N were ranging from 4.64 in March to 10.84 in February.

The pH values ranged values between 6.63 (acidic) in March and 6.97 (quite neutral) in January. The contents of TN ranged from 0.52 to 2.03 %. The TP lowest value was 0.98 % (March) and the highest value was 1.97 % (January). Records of C/N ratio ranged from 6.97 (February) to 15.07 (March) due to the difference of OC % contents (Table 4) (Figure 4).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.97

6.84

6.63

6.63

6.97

---

0.171

OM%

20.12

45.26

13.25

13.25

45.26

26.21

16.851

OC%

11.64

26.25

7.84

7.84

26.25

15.24

0.719

TN%

1.67

2.03

0.52

0.52

2.03

1.40

0.988

C/N

6.97

12.93

15.07

6.97

15.07

11.65

4.197

TP%

1.97

1.82

0.98

0.98

1.97

1.59

0.533

Table 4 Monthly Variations in the Sludge Properties at Station 4

Figure 4 Records of C/N ratio ranged from 6.97 (February) to 15.07 (March).

The pH values ranged between 6.32 (acidic) in February and 7.27 (neutral) in January. The OM concentration ranged between17.83 % (March) and 24.20 % (February). The TN contents ranged between 2.99 and 4.17 %. The TP contents were 0.97 % (March) and 2.01 % (February). The C/N ratio were ranging from 2.47 (March) to 4.69 (February) due to a decrease in the TN % contents relative to an increase in the OC % contents (Table 5) (Figure 5).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.27

6.32

6.96

6.32

7.27

---

0.484

OM%

21.89

24.2

17.83

17.83

24.20

21.30

3.224

OC%

12.67

14.04

10.34

10.34

14.04

12.35

1.870

TN%

3.07

2.99

4.17

2.99

4.17

3.41

0.659

C/N

4.12

4.69

2.47

2.47

4.69

3.76

1.152

TP%

1.06

2.01

0.97

0.97

2.01

1.34

0.576

Table 5 Monthly Variations in the Sludge Properties at Station 5

Figure 5 The C/N ratio were ranging from 2.47 (March) to 4.69 (February).

The pH values ranged between 6.51 (acidic) in March and 7.32 (slightly basic) in January. The OM contents ranged between 20.93% (January) and 23.9 % (March). Contents of TN and TP were increasing during the study period, showing ranges of (2.78-4.57 %) for TN and (0.52-3.23 %) for TP. For both, the highest values were obtained in March, while the lowest values were obtained in January. The C/N ratios were decreasing with range from 4.73 in January to 3.04 in March (Table 6) (Figure 6).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.32

6.87

6.51

6.51

7.32

---

0.405

OM%

23.45

20.93

23.90

20.93

23.90

22.76

1.60

OC%

13.15

12.11

13.90

12.11

13.90

13.05

0.898

TN%

2.78

3.74

4.57

2.78

4.57

3.69

0.895

C/N

4.73

3.24

3.04

3.04

4.73

3.67

0.923

TP%

0.52

1.91

3.23

0.52

3.23

1.88

1.355

Table 6 Monthly Variations in the Sludge Properties at Station 6

Figure 6 The C/N ratios were decreasing with range from 4.73 in January to 3.04 in March.

The pH values ranged from 6.20 (acidic) in March to 7.39 (alkaline) in January may be due to wastewater composition. The OM contents decreased from 37.34 in January to 12.8 in March. Contents of each of TN and TP were highest in March with ranges (1.91-2.33 %) for TN and (1.21-1.92 %) for TP. A wide range of the C/N ratio was recorded due to the different content of OC % reported. The differences in C/N ratios were ranging from 3.18 (March) to 10.43 (February) (Table 7) (Figure 7).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.39

6.82

6.20

6.20

7.39

---

0.595

OM%

37.43

26.71

12.80

12.80

37.43

25.64

12.349

OC%

21.71

15.46

7.42

7.42

21.71

14.86

7.163

TN%

2.08

1.91

2.33

1.91

2.33

2.10

0.211

C/N

10.43

18.09

3.18

3.18

18.09

7.23

3.700

TP%

1.21

1.71

1.92

1.21

1.92

1.61

0.364

Table 7 Monthly Variations in the Sludge Properties at Station 7.

Figure 7 The differences in C/N ratios were ranging from 3.18 (March) to 10.43 (February).

Values of pH ranged from 6.43 to 7.30, covering all of the slightly acidic, neutral state and slightly alkaline sides. This may be related to wastewater composition. The highest pH value was recorded in January, while the lowest value was recorded in February. The OM content was increasing from 17.58 % (January) to 28.07 % (March). Contents of TN and TP showed average values of (2.67±0.25) for TN and (2.09±0.12) for TP. The C/N ratios were ranging from 4.81 to 5.80. (Table 8) (Figure 8)

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.30

6.43

7.09

6.43

7.30

---

0.453

OM%

17.54

23.71

28.07

17.54

28.07

23.10

5.290

OC%

13.57

13.75

16.28

13.57

16.28

14.53

1.513

TN%

2.82

2.37

2.82

2.37

2.82

2.67

0.259

C/N

4.81

5.80

5.77

4.81

5.80

5.46

0.563

TP%

2.21

1.97

2.10

1.97

2.21

2.09

0.120

Table 8 Monthly Variations in the Sludge Properties at Station 8

Figure 8 The C/N ratios were ranging from 4.81 to 5.80.

The highest value of pH was recorded in January (7.57) and the lowest value was recorded in March (6.93). The OM content ranged between 14.25 % (January) and 18.57 % (March). Contents of TN showed values between 0.92 % (March) and 2.18 % (January). TP contents showed values between 0.59 % (January) and 1.68 % (March). The C/N ratios ranged between 3.78 and 11.77 (Table 9) (Figure 9).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.57

---

6.93

6.93

7.57

---

0.452

OM%

14.25

---

18.67

14.25

18.67

16.46

3.125

OC%

8.26

---

10.83

8.26

10.83

9.54

1.817

TN%

2.18

---

0.92

0.92

2.18

1.55

0.890

C/N

3.78

---

11.77

3.78

11.77

7.77

5.649

TP%

0.59

---

1.68

0.59

1.68

1.13

0.770

Table 9 Monthly Variations in the Sludge Properties at Station 9

Figure 9 The C/N ratios ranged between 3.78 and 11.77.

The pH values changed from 6.77 (in January) to neutral state 7.03 (in February). The OM contents ranged from 55.25 to 57.45. The distribution of TN (%) was ranging from 4.97 to 5.29, while the range of TP content (%) was from 0.98 to 1.07. The C/N records ranged from 6.28 to 6.43; this similarity is due to the constant contents of each of OC % and TN % at this station during the study period (Table 10) (Figure 10).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.77

7.03

---

6.77

7.03

---

0.183

OM%

57.47

55.25

---

55.25

57.47

56.36

1.560

OC%

33.27

31.98

---

31.98

33.27

32.62

0.912

TN%

5.29

4.97

---

4.97

5.29

5.13

0.226

C/N

6.28

6.43

---

6.28

6.43

6.35

0.106

TP%

1.07

0.98

---

0.98

1.07

1.02

0.063

Table 10 Monthly Variations in the Sludge Properties at Station 10

Figure 10 The C/N records ranged from 6.28 to 6.43.

The pH values ranged between 6.60 in January and 6.69 March. The OM contents ranged from 30.72 % (March) to 31.45 % (January). The contents of TN were ranging from 0.96 % to 1.92 % whereas the contents of TP were ranging from 0.85 % to 1.35 %. The C/N ratio showed a wide range of from 9.26 % (January) to 19 % (March) due to the different content of TN % reported at this station during the study period (Table 11) (Figure 11).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.60

---

6.69

6.60

6.69

---

0.063

OM%

30.72

---

31.45

30.72

31.45

31.08

0.516

OC%

17.87

---

18.24

17.78

18.24

18.01

0.325

TN%

1.92

---

0.96

0.96

1.92

1.44

0.678

C/N

9.26

---

26.43

9.26

26.43

17.84

12.14

TP%

1.35

---

0.85

0.85

1.35

1.10

0.353

Table 11 Monthly Variations in the Sludge Properties at Station 11

Figure 11 The C/N ratio showed a wide range of from 9.26% (January) to 19% (March).

The pH values ranged between acidic side (6.06 in January) and alkaline side (7.97 in March), due to wastewater composition. The OM contents were increasing from 30.70 % (March) to 37.12 % (January). The TN contents were decreasing from 4.42 to 1.79 %, and its average was (2.92±1.3). The TP contents showed a lowest value reported in January (1.05 %) and a highest value was obtained in Mach (1.43 %). The C/N ranged from 4.86 to 12.55 (Table 12) (Figure 12).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.06

7.27

7.97

6.06

7.97

---

0.887

OM%

37.12

34.26

30.70

30.70

37.12

34.02

3.216

OC%

21.49

19.88

17.77

17.77

29.88

23.04

6.203

TN%

4.42

2.38

1.79

1.79

4.42

2.92

1.312

C/N

4.86

12.55

9.02

4.86

12.55

8.81

3.849

TP%

1.05

1.22

1.43

1.05

1.43

1.23

0.190

Table 12 Monthly Variations in the Sludge Properties at Station 12

Figure 12 The C/N ranged from 4.86 to 12.55.

The pH values ranged between 6.79 in February and 7.14 in January. The OM contents were decreasing from 32.46 % (January) to 23.29 % (March). The TN contents were decreasing from 2.78 % to 1.87 % and the contents of TP were increasing from 0.52 to 1.89 %. The C/N ratio ranged from 6.21 (March) to 7.29 (February) due to that both OC % and TN % content were decreasing during the study period (Table 13) (Figure 13).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.14

6.79

7.06

6.79

7.14

---

0.183

OM%

32.46

27.97

23.29

23.29

32.46

27.90

4.585

OC%

18.79

16.19

13.48

13.48

18.79

16.15

2.655

TN%

2.78

2.22

1.87

1.87

2.78

2.29

0.459

C/N

6.75

7.29

6.21

6.21

7.29

6.75

0.540

TP%

0.52

0.93

1.89

0.52

1.89

1.11

0.703

Table 13 Monthly Variations in the Sludge Properties at Station 13

Figure 13 The C/N ratio ranged from 6.21 (March) to 7.29 (February).

The pH values reached to 7.02 and 7.05 in January and February (almost neutral). The OM contents ranged between 21.14 % (February) and 23.12 % (January). The distribution of TN (%) was ranging from 2.69 to 2.73, while the range of TP contents (%) was from 2.58 to 2.73. The records of C/N ratio were ranging from 4.55 to 4.90, due to the almost constant contents of each of OC % and TN % during the study period (Table 14) (Figure 14).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.05

7.02

---

7.02

7.05

---

0.212

OM%

21.14

23.12

---

21.14

23.12

22.13

1.400

OC%

12.26

13.38

---

12.26

13.38

12.82

0.791

TN%

2.69

2.73

---

2.69

2.73

2.71

0.020

C/N

4.55

4.90

---

4.55

4.90

4.72

0.247

TP%

2.73

2.58

---

2.58

2.73

2.65

0.106

Table 14 Monthly Variations in the Sludge Properties at Station 14

Figure 14 The records of C/N ratio were ranging from 4.55 to 4.90.

Neutral pH values obtained ranging between 6.98 in January and 7.17 in March. The OM contents were in the range of 19.97 % (February) and 22.21 % (March). The contents of each of TN and TP are in the ranges (3.07-3.34 %) and (1.04-1.87 %), respectively. The C/N ratio ranged between 3.46 to 3.98, due to the almost constant contents of each of OC % and TN % at the station (Table 15) (Figure 15).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

6.98

7.12

7.17

6.98

7.17

---

0.098

OM%

20.87

19.97

22.21

19.97

22.21

21.01

1.12

OC%

12.08

11.56

12.85

11.56

12.85

12.16

0.649

TN%

3.07

3.34

3.23

3.07

3.34

3.21

0.135

C/N

3.93

3.46

3.98

3.46

3.98

3.79

0.286

TP%

1.04

1.52

1.87

1.04

1.87

1.47

0.416

Table 15 Monthly Variations in the Sludge Properties at Station 15

Figure 15 The C/N ratio ranged between 3.46 to 3.98.

The pH values ranged between neutral (7.25) in January and acidic (6.23) in February. The OM contents showed values between 27.9 % (February0 and 29.9 % (January). The TN was ranging from 3.53 to 4.69 and the TP contents were ranging from 1.29 % to 5.53 %. The C/N ratios were ranging from 3.70 to 4.56 due to the almost similar contents of both of OC % and TN % at this station during the study period (Table 16) (Figure 16).

Parameter

Jan.

Feb.

Mar.

Min.

Max.

Average

STD Deviation

pH

7.25

6.23

---

6.23

7.25

---

0.722

OM%

29.93

27.81

---

27.93

29.93

28.87

1.499

OC%

17.36

16.10

---

16.10

17.36

16.73

0.890

TN%

4.69

3.53

---

3.53

4.69

4.11

0.820

C/N

3.70

4.56

---

3.70

4.56

4.13

0.608

TP%

5.53

1.29

---

1.29

5.53

3.41

2.99

Table 16 Monthly Variations in the Sludge Properties at Station 16

Figure 16 The C/N ratios were ranging from 3.70 to 4.56.

Conclusion

  1. The wide ranges of sludge properties were mostly related to the variations in types of pumping stations, nature of surrounding area and illegal connections of sewage.
  2. Sludge collected from each station had similar pH values and much more variations in the sludge properties and organic matter composition.

Acknowledgements

None.

Conflict of interest

The author declares no conflict of interest.

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