There is no truer sign of civilization and culture than good sanitation. A good drain reflects the culture as much as a beautiful statue [1,2]. Wastewater is essentially the water supply of the community after it has been fouled by a variety of uses. The water supplied to a community receives a range of chemical substances and microbial flora during its use such that the wastewater acquires a polluting potential and becomes a health and environmental hazard. Communicable diseases of the intestinal tract such as cholera, typhoid, dysenteries and water borne diseases like infectious hepatitis etc., can be spread from uncontrolled disposal of wastewater, and therefore prevention of communicable diseases and protecting public health attracts the primary objective of sanitary wastewater disposal [2,3].

The sites for disposal of wastewater have traditionally been natural watercourses, land and the coastal waters. One of the major sources of organic pollution is effluents from sewage treatment works. Prevention of pollution of natural resources such as land and water by the wastewater and adequate preparation or renovation of the wastewater before reuse, are further important considerations in formulating and designing appropriate wastewater disposal arrangements [3,4].

Given the characteristics of raw wastewater and the requirements of disposal or reuse, the wastewater usually requires some type of preparation or treatment before it is rendered fit for disposal or reuse. Generally, in many situations involving domestic wastewater, the treatment consists of removal of suspended solids and 5-day, 20°C BOD, which are the two usual parameters of prime interest. The degree of treatment provided to the wastewater will largely be based on the effluent standards prescribed by the regulatory agencies when the treated effluent is to be discharged into a watercourse or land. If the effluent is to be reused, the quality of the effluent required to support such reuse will indicate the degree of treatment necessary. The complete treatment of wastewater is brought by a sequential combination of various physical unit operations, and chemical and biological unit processes. The general yardstick of evaluating the performance of sewage treatment plant is the degree of reduction of BOD, and suspended solids, which constitute organic pollution. The performance efficiency of treatment plant depends not only on proper design and construction but also on good operation and maintenance [5,6].

Performance evaluation of existing treatment plants is required (1) to assess the existing effluent quality and/or to meet higher treatment requirements and, (2) to know about the treatment plants whether it is possible to handle higher hydraulic and organic loadings. Performance appraisal practice of existing treatment plants is effective in generation of additional data which also can be used in the improvement in the design procedures to be followed for design of these plants. Existing facilities can be made to handle higher hydraulic and organic loads by process modifications, whereas meeting higher treatment requirements usually requires significant expansion and/or modification of existing facilities [7,8].

One of the primary considerations in evaluating an existing wastewater treatment plants is in the area of plant operation and control. A major tool required for proper process control is frequent and accurate sampling and laboratory analysis [9,10].

In the current wastewater treatment process, microorganisms play a significant role in the treatment of domestic sewage. Many different organisms live within the wastewater itself, assisting in the breakdown of certain organic pollutants [11,12]. The basis for using these EM species of microorganisms is that they contain various organic acids due to the presence of lactic acid bacteria, which secrete organic acids, enzymes, antioxidants and metallic chelates. The creation of an antioxidant environment by EM assists in the enhancement of the solidliquid separation, which is the foundation for cleaning water [13,14].

Poor conditions of sewerage system, improper design of the plant and organizational problems are important factors that cause treatment plant not to meet the effluent standards [14]. Overloading due to increase in population and water use, discharge of trade effluents are other reasons of recent times for the poor performance of wastewater treatment plants [15]. The treatment efficiency may be badly affected if the system is hydraulically under loaded [14-18].

The main aims of the present study are to study and evaluate the wastewater treatment plants efficiency in Garbyia Governorate.

Case of the study

The study aimed to evaluate the performance and efficiency of the Wastewater Treatment Plants (WWTPs) in El-Gharbia Governorate, middle of Delta, Egypt as shown in Figure 1. The survey of present study covers more than 90% of the WWTPs in El-Gharbia governorate (17 WWTPs; Tanta, Mahalet Marhom, Fesha, Nawag, Nefia, Mahalet Menof, Berma, Basyoun, Mashal and Kom Elnagar, Kafr Elzayat, Kotour, Neshyl, Segen Elcoom, Elsanta, Zefta, Elmahala Elkobra, and Saft Trab). El-Gharbia Governorate WWTPs were designed and constructed in order to receive an average of 493500 m3 of raw sewage wastewater per day aimed to manage it so as to minimize and/or remove organic matter, solids, nutrients, disease-causing organisms and other pollutants before it mixed with surface water bodies according to law No. 48 of 1982 and amendments. WQI were calculated as shown in Table 1.

Figure 1: Sampling sites, El-Gharbia Governorate.

Table 1: Water Quality Index (WQI) weights and calculation.

Sampling

The collected samples were carried out during the study period (Jan. to Dec. 2016), collection and storage of samples were carried out according to APHA [19-21].

Performance appraisal has been carried out by comparing the concentrations of pollutants at the influent and effluent of the investigated treatment plants. The grab and composite samples were collected at the influent and effluent of the investigated treatment plants in clean polyethylene bottles. Composite samples were collected over 12 hours at a rate of one sample each hour. Residual chlorine (R.Cl₂) was measured on site during sampling time. The composite samples were analysed for various parameters like BOD₅, COD and TSS. The samples were analysed as outlined in the standard methods for the examination of water and wastewater APHA, Depending on the results, performance of each plant was evaluated. By regression analysis correlations between TSS, COD and BOD₅ were established to improve treatment plants control and operation.

The evaluation of performance (pollutant removal efficiency) of the investigated wastewater treatment plants was undertaken in terms of effluent quality. The evaluation was based on measurements of TSS, BOD₅, COD, R.Cl2, plant TSS removal efficiency (TSS%), plant BOD₅ removal efficiency (BOD₅%), and influent COD/BOD₅ ratio. These parameters were estimated on monthly basis for the raw untreated wastewater (influent) and treated wastewater (effluent) for the period of 12 months from January to December, 2016.

TSS, BOD₅ and COD

TSS, BOD₅ and COD are indirect indicators for total suspended solids, fermentable and non-fermentable organic content. The obtained data show that, the physical (TSS), chemical (COD) and biochemical (BOD₅) properties of the influent exhibits insignificant variations among the different investigated WWTPs. This variation trend was also detected for the single plant at different times. This variation may attribute to the different social, economic, geographic and climatic conditions in the studied communities. Significant variations of physical, chemical and biochemical properties of the different investigated WWTPs effluent were observed. This variation can be ascribed to the nature of incoming organic loading, the type of the operational conditions and mainly the difference in the efficiency of the treatment process.

The observed variability of the effluent concentrations and the removal efficiencies within all treatment plants operates with different technologies, considering all the analyzed constituents can be visualized in the data presented in the present study. These results are in agreement with the results obtained by Oliveira and Von Sperling.

The present results demonstrate that, Kotour WWTP operates with the oxidation ditch technology exhibits the highest performance efficiency, while Tanta WWTP operates with conventional activated sludge technology exhibits the lowest one.

TSS and TSS removal efficiency

TSS: The data of TSS are recorded in Tables 2 and 3. For the investigated WWTPs the average influent values of TSS are ranged from 253.167 mg/L at Mahalet Menof WWTP to 111.250 mg/L at El Mehala El Kobra WWTP. The average effluent values of TSS are ranged from 24.583 mg/L at Kotour WWTP to 144.583 mg/L at Tanta WWTP. These results reveal that the influent of the investigated WWTPs presents means of TSS significantly higher than that presented by the effluent. As well as the present results indicate that there is no significant variation in the influent mean TSS values while there is a significant variation in those presented by the effluent. A poor performance was observed for Tanta, Nefia, and Elmahala Elkobra, WWTPs. On the other hand, a good performance was detected for Mahalet Marhom, Fesha Sleem, Mahalet Menof, Berma, Basyoun, and Kom Elnagar, Kafr Elzayat, Kotour, Neshyl, Elsanta, and Elkorashia, Shenrak, Elgafaria, Zefta, Nawag, Saft Trab and Elhyatem WWTPs.

Table 2: TSS data (mg/L) of the influent and effluent of the WWTPs. All data represents means of five replicates ± Stander Deviation (SD), TSS: Total suspended solids, IN: Influent (untreated raw wastewater) and E: Effluent (treated wastewater).

Table 3: Mean TSS removal efficiency of the thirty investigated WWTPs. All data represents means of 12 replicates per year ± Standard Deviation (SD), TSS: Total suspended solids, IN: Influent (untreated raw wastewater), E: Effluent (treated wastewater) and *: Significant variation.

The results show that, all collected samples from Tanta, El Mehala El Kobra and Nawag WWTPs were exceeding the Egyptian Permissible limits (TSS: 40 mg/l) while the samples collected from Mehalet Menof, Kotour, El Santa, Shernak and Zefta were complying the Egyptian regulations as indicated in Table 10.

Horan et al. defined the activated sludge process as a suspended growth system comprising a mass of microorganisms constantly supplied with organic matter and oxygen. This process is widely used worldwide for the treatment of domestic and industrial wastewater, in situations where high effluent quality is necessary [22,23]. According to Francioso et al. a number of AS processes and design configuration have evolved due to new regulations for effluent quality, technological advances, better understanding of microbial processes and to reduce costs. We can have complete-mix activated sludge (CMAS), plug-flow (conventional, high-rate aeration, step feed, contact stabilization, twosludge, high-purity oxygen, Kraus process, conventional extended aeration), extended aeration (oxidation ditch, orbal, countercurrent aeration system, biolac process) and the sequentially operated systems such as sequentially batch reactor (SBR), cyclic activated sludge system (CAAS), Batch decant reactor- intermittent cycle extended aeration system (ICEAS) (Figures 2 and 3).

Figure 2: TSS of Tanta WWTP during the present study.

Figure 3: TSS of Elsanta WWTP during the present study.

TSS removal efficiency

The data obtained for the TSS removal efficiency in Tables 3 and 4 illustrate that the average removal of TSS is ranged from 51.1% to 91.5% for Tanta and Kotour WWTPs respectively. Kotour WWTP is more efficient than Tanta WWTP in TSS removal by 40.38%. Poor efficiency for TSS removal is detected for Tanta, Nawag, Nefia, and Elmahala Elkobra, WWTPs. These results reveal a significant variation in the mean TSS removal efficiency for all investigated WWTPs.

Table 4: Influent and effluent BOD₅ values (mg/L) of the thirty investigated WWTPs.All data represents means of five replicates ± Stander Deviation (SD), BOD₅: Biochemical oxygen.

BOD₅ and BOD₅ removal efficiency

BOD₅: Table 4 presents the BOD₅ values (mg/L) for the influent and effluent of the investigated WWTPs. Table 5 shows the mean BOD₅ values (mg/L) for the influent and effluent of the thirty investigated WWTPs. For the investigated WWTPs, the average influent values of BOD₅ are ranged from 330.833 mg/L to 399.167 mg/L for Segen Elcoom and El Moutamadia WWTPs respectively. The average effluent values are ranged from 34.833 mg/L to 181.500 mg/L for Shenrak and Tanta stage 2 WWTPs respectively. These results indicate poor performance for Tanta, and Elmahala Elkobra WWTPs. A good performance is detected for Mahalet Marhom, Fesha Sleem, Mahalet Menof, Berma, Basyoun Mashal and Kom Elnagar, Kafr Elzayat, Kotour, Neshyl, Elsanta, Shenrak, and Zefta, WWTPs.

Table 5: BOD₅ removal efficiency (%) of the thirty investigated WWTPs.All data represents means of five replicates ± Stander Deviation (SD), BOD₅: Biochemical oxygen demand after five days, IN: Influent (untreated raw wastewater) and E: Effluent (treated wastewater).

It is obvious that the influent of the investigated WWTPs presents means of BOD₅ significantly higher than that presented by the effluent. No significant variation in the influent mean BOD₅ values can be detected while there is a significant variation in those presented by the effluent.

The results show that, all collected samples from Tanta, and El Mehala El Kobra WWTPs were exceeding the Egyptian Permissible limits (BOD: 60 mg/l) while the samples collected from Mehalet Menof, Nawag, Menof, Kotour, El Santa, Shernak and Zefta were complying the Egyptian regulations as indicated in Table 12.

BOD₅ removal efficiency

Table 5 presents the BOD₅ removal efficiency (%) of the investigated WWTPs. Table 6 presents the mean BOD₅ removal efficiency of the thirty studied WWTPs. The average values of BOD₅ removal efficiency are ranged from 52.3% to 90.1% for Tanta and Kotour WWTPs respectively. Kotour WWTP is more efficient than Tanta WWTP in BOD₅ removal by 37.72%. Poor BOD₅ removal efficiency is observed for Tanta, Nawag, Nefia, Elmahala Elkobra, Saft Trab and Elhyatem WWTPs. A significant variation in the mean BOD₅ removal efficiency for the investigated WWTPs is observed (Figures 4 and 5).

Table 6: Influent and effluent COD values (mg/L) of the thirty investigated WWTPs. All data represents means of five replicates ± Stander Deviation (SD), COD: Chemical oxygen demand, IN: Influent (untreated raw wastewater) and E: Effluent (treated wastewater).

Figure 4: BOD of Tanta WWTP during the present study.

Figure 5: BOD of Elsanta WWTP during the present study.

Dissolved organics are generally treated with biological processes. The more common systems are aerobic (with oxygen) and include aerobic or facultative pond, biofilm reactor, and activated sludge processes. All these processes rely on the ability of microorganisms to convert organic wastes into stabilized, low-energy compounds [15].

COD of the investigated WWTPs

Table 6 shows the influent and effluent COD values (mg/L) of the investigated WWTPs. Table 6 reports the mean influent and effluent COD values (mg/L) of the investigated WWTPs. The average values of the influent COD are ranged from 657.42 mg/L to 663.08 mg/L for Tanta and Neshyl WWTPs respectively. The average effluent values are ranged from 57.417 mg/L to 253.333 mg/L for Shenrak and Elmahala Elkobra WWTPs respectively.

These results show a poor performance for Tanta, Nefia, Elmahala Elkobra, Nawag, Saft Trab WWTPs. A good performance is detected for Mahalet Marhom, Fesha Sleem, Mahalet Menof, Berma, Basyoun Mashal and Kom Elnagar, Kafr Elzayat, Kotour, Neshyl, Elsanta, Shenrak, and Zefta, WWTPs.

The present results illustrate that the influent of the investigated WWTPs presents means of COD significantly higher than that presented by the effluent. No significant variation in the influent mean COD values is observed, while there is a significant variation in those presented by the effluent.

The results show that, all collected samples from Tanta, and El Mehala El Kobra WWTPs were exceeding the Egyptian Permissible limits (COD: 80 mg/l) while the samples collected from Mehalet Marhom, Mehalet Menof, Kotour, El Santa, Shernak and Zefta were complying the Egyptian regulations as indicated in Table 11.

Chemical oxygen demand (COD) is a measure of the amount of oxygen required to chemically oxidize reduced minerals and organic matter [22,23]. Higher levels of COD were observed in influent but were reduced, with a mean percentage removal efficiency of 38.9 (± 62.22) % in effluent in average. This explains the significant difference between influent and effluent values of BOD as a result of plants performance (P>0.05). Furthermore, COD effluent concentrations were above the recommend EPA standard of 250 mg/L despite high percentage removal efficiency. This is due to very low algal populations to cause chemical activity that will reduce the COD [24,25] (Figures 6 and 7).

Figure 6: COD of Elsanta WWTP during the present study.

Figure 7: COD of Elsanta WWTP during the present study.

Residual chlorine (R.Cl2)

Table 7 reveals the effluent R.Cl2 values (mg/L) of the investigated WWTPs. Data in Table 8 provides the mean values of the effluent R.Cl2 (mg/L) of the investigated WWTPs. Mean effluent R.Cl2 values below the reference value is observed for Tanta, Kom Elnagar, Neshyl, Shenrak, and Saft Trab WWTPs. A significant difference in the effluent R.Cl2 values of the investigated WWTPs were noticed.

Table 7: Effluent R.Cl2values (mg/L) of the thirty investigated WWTPs. All data represents means of five replicates ± Stander Deviation (SD), R.Cl2: Residual chlorine, IN: Influent (untreated raw wastewater) and E: Effluent (treated wastewater).

Influent COD/BOD₅ ratio: Table 8 presents the influent COD/ BOD₅ ratio of the investigated WWTPs. Data in Table 9 reports the mean influent COD/BOD₅ ratio of the investigated WWTPs. The values of the influent COD/BOD₅ ratio of the investigated WWTPs are within the normal range and does not exceeded the upper reference value reported by Wentzel et al. [11] (1.25-2.5). This indicates that the incoming influents to these investigated WWTPs are human wastes in nature and is not industrial wastes. Industrial wastes are characterized by the presence of slowly biodegradable organic suspended solids or refractory substances for biodegradation or both of them. These results indicate a non-significant variation in the mean influent COD/BOD₅ ratio of the studied WWTPs.

Table 8: Mean influent COD/BOD₅ ratio of the thirty investigated WWTPs.All data represents means of 12 replicates per year ± Standard Deviation (SD), BOD₅: Biochemical oxygen demand after five days, COD: Chemical oxygen demand, IN: Influent (untreated raw wastewater).

It can be observed that, the influent COD/BOD₅ ratio are lower than 3. This indicates that these influent wastewaters can usually be successfully treated with biological processes because of their high biodegradability and this meets the data reported by Ng Wun [25].

Correlations developed between TSS, COD and BOD₅: Establishment of constant relationships among the various measures of organic content depends primarily on the nature of the wastewater and its source. Variations of both influent and effluent BOD₅ with the influent and effluent TSS and COD were achieved using regression analysis (Table 9). As the experimental determination of BOD₅ requires relatively long time (5 days), this theoretical correlation gives a fast expectation for the corresponding BOD₅ values. Once the correlation has been established, TSS and COD measurements can be used to provide a good advantage for treatment plant control and operation. This will improve the performance efficiency of the investigated WWTPs [26,27].

Table 9: Correlations developed between TSS, COD and BOD₅ of the thirty investigated WWTPs. TSS: Totalsuspended solids, BOD₅: Biochemical oxygen demand after five days, COD: Chemical oxygen demand and R Square: Coefficient of determination.

Treated water quality index and data analysis: Table 13 and Figure 8 show the calculated values of WQI for treated wastewater of the investigated WWTPs in the Garbyia Governorate. The values of WQI ranged from 69 (Neshyl WWTP) to 143 (Mehala El Kobra WWTP).

Table 13: WQI for WWTPs.

Figure 8: WQI for WWTPs.

Data Analysis

Tables 10-12 shows the number of collected samples and didn’t comply with Egyptian guidelines values for TSS, BOD and COD (Figure 8).

Table 10: TSS data analysis.

Table 11: COD data analysis.

Table 12: BOD data analysis.

The performance studies on the investigated sewage treatment plants located in El-Gharbia governorate in Egypt conducted for a period of 12 months reveal that the overall performance achieved by some of the investigated plants is lower than the expected performance. This shows that improvements in the current situation are possible, thus serving as an incentive to designers and plant operators. Nonsignificant variation in the influent’s mean TSS, BOD₅, COD and COD/ BOD₅ ratios are observed. While significant variations in the removal efficiencies and the effluent concentrations considering all the analyzed constituents are obtained during the experimental period within all investigated treatment plants. The influents of the investigated WWTPs are human wastes in nature and can usually be successfully treated with biological processes because of their high biodegradability. Theoretical correlations between influents and effluents TSS, COD and BOD₅ were determined. These correlations can be used to provide a good advantage for treatment plant control and operation. A probabilistic model has been used for determining achievable effluent BOD₅, COD and TSS concentrations. This probabilistic approach provides a theoretical basis for the analysis of reliability. The reliability measures are expressed in probability terms, that is, the probability of success or adequate performance as a function of mean values and effluent variability. The effluent variability has been described by the coefficient of variation. The performance variability in some WWTPs are observed, this is because there are many factors that affect wastewater treatment plant performance (reliability). Flow variability and their characteristics, the inherent variability of the behavior of wastewater treatment processes (inherent reliability), the variability caused by failures, in addition the lack of experience of the wastewater treatment plant operators especially in the developing countries.