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

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).

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

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

$TS(as\%of wet sludge)=\frac{wt\text{'}}{wt}(100)$
Where wt' is weight of sample after drying; wt is weight of sample before drying.

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.

$Volatile matteer (as \% of dried solids) = \frac{wt\text{'}}{wt} (100)$
where wt' is weight lost during ignition; wt is weight remaining after drying.

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

$N=\frac{10}{V_{blank}}$
Percentage OM in sludge:

% Total OC $\left(\frac{w}{w}\right)$  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
V_blank = Volume of ferrous ammonium sulfate solution required to titrate the blank (in ml)
V_sample = 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.

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
$wt\text{'}=\frac{v x 0.14}{1}\left(100\right)$
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.

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.

$Conc.of\left(P\right)=\frac{\left(Abs\times F_1\times D\right)}{wt}$
Where Abs = absorbance of sample solution; F1 = factor of standard curve (x/y); D = Dilution factor; wt = weight of sample after ignition.

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).

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).

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).

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).

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).

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).

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).

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)

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).

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).

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).

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).

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).

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).

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).

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).

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

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.

None.

The author declares no conflict of interest.

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