Background and Sewage sludge can supply nutrients and improve soil condition. However, presence of microorganisms, particularly parasites could cause a variety of diseases in humans and animals. This study aimed at identifying parasites in the waste sludge of industrial sewage in Babolsar, north of Iran and comparing their concentration with the EPA standards.
Sampling was conducted in the sludge sewage treatment plant in one industrial town from four sludge depot during six months. Nine samples were taken from each depot. In order to identify the parasites McMaster slide was used according to Bailenger method.
This study showed that the average numbers of helminth eggs in pallets 1, 2, 3, and 4 were 4.42, 17.52, 7.65, and 7.3 per 4 grams dried sludge, respectively. The greatest numbers of helminth eggs, was associated with Toxocara and Hymenolepis diminuta.
In current investigation, the number of helminth eggs in the sludge was higher than that suggested by the EPA standards. The sludge studied was industrial, therefore, the possibility of parasitic infection caused by people is low. On the other hand, the numbers of Hymenolepis diminuta and Toxocara were high. As a result, the possibility of secondary pollution due to movement of animals is high.

Background and Currently, there is only one sewage treatment plant in Sercan City in Hamadan province. Extended aeration activated sludge is the main process of the plant and untreated effluent and disposal sludge are used for agricultural activities. The main objective of this research is to evaluate the stabilization degree and reuse potential of disposal sludge from the plant. This study was undertaken over a 12 months period from March 2001 to March 2002. In this project some indexes of sludge stabilization and reuse including VS/TS ratio, pH, SOUR, floatation, color, odor, coliform and fecal coliform were determined. The annual average ratio of VS/TS and SOUR in disposal sludge from this plant were 0.73 and 3.37 mg02/gr.vs.h, respectively. The average pH was about 7. The disposal sludge was septic and had dark brown color and floated after a short time. Also the annual average of fecal coliform density in disposal sludge was 8.97 ´ 107 MPN/g.ds. The disposal sludge was raw and destabilized. The microbial quality of disposal sludge was lower than the class B of USEPA regulation. Therefore, this sludge can not be discharged to environment or reused.

Sludge drying bed is preferred to mechanical methods due to the need for very simple technology. Due to restriction of natural dewatering, we tried to eliminate some of these limitations by the tests and studies of assumptions. In this study, the effect of hydrostatic suction and sludge chemical conditioning has been studied in the natural sludge dewatering optimization. At first, hydrostatic suction created by water entry and exit control, then by adding ferric chloride in the optimum dosage to the aerobic digested sludge, dewatering process was compared with the control bed. Retention time of the sludge cake and quality of effluent from the drainage layer were compared with control pilot. The retention time of sludge cake decreased from 5 days to 2 days and by using inorganic agent with the consistency of 440 mg/lit to the aerobic digested sludge conditioning, it's retention time (production of sludge with the dry solids consistency of 45 percent) decreased from 6 days to 3 days. The third stage of experiment was simultaneous use of chemical conditioning and hydrostatic suction in drying bed and its result was very satisfactory.Use of Hydrostatic suction can improve physical and chemical characteristics of effluent from the output of bed, such as turbidity, pH, TSS and VSS, while it increases COD and TDS. It should be mentioned that sludge chemical conditioning, increase effluent factors like TS and TDS.

In the present research, the effect of different coagulants in conditioning of digested sludge in Qods wastewater plant, have been investigated. In order to accomplish such investigation, coagulants including cationic polyelectrolyte, feeric chloride, quicklime and alum, with different concentrations, were added to the sludge samples. Jar test, then specific resistance of sludge with respect to dewatering, TSS and VSS on sludge samples before and after dewatering were performed. In addition, TSS and VSS, COD, BOD5 and turbidity were performed on supernatant in order to determine the optimized concentration of The value of specific resistance of sludge to the dewatering process for raw sludge and conditioned sludge with cationic polyelectrolyte, ferric chloride, ferric chloride with lime, lime and alum are as follows: 7.68*1013, 0.347*1013, 0.839*10113, 0.89*1013,, 2.36*1013 and 2.52*1013 m/kg. Since my decrease in specific resistance of sludge facilities the dewatering process, it could be concluded that the most suitable for fludge conditioning are, cationic polyelectrolyte, ferric chloride, ferric chloride with lime, lime and alum respectively.By considering the results of this investigations and comparing economic factors and supplier availability, ferric chloride as pilot sludge conditioner substance was preferred. By adding ferric with concentration of 440 mg/l to the outgoing sludge from aerobic digester, the required time for drying sludge (production of sludge with DS=45%) in drying beds, is reduced from 9 days to 4 days. In other word, if input sludge to drying beds in conditioned, the required bed area, is reduced considerably (at least 50%).

Sludge treatment and disposal processes in wastewater treatment plants account for a significant portion of the total treatment costs. One of the most expensive parts of sludge treatment is chemical conditioning. Study of the effect of process chain on the conditioning and dewaterability can effectively optimize and reduce operating costs and increase the quality of effluent sludge. This paper investigates the impact of aerobic digestion of waste sludge in Yazd wastewater treatment plant by SBR method on its dewaterability. For this purpose, the waste sludge sample of the plant was aerated in the laboratory at different residence times from 1.5 to 7 days. Then the dewaterability of the sludge was measured by two methods of Specific Resistance to Filtration (SRF) and Tests of Time of Filtration (TTF) in two cases with and without chemical conditioning with cationic polyacrylamide. The results showed that sludge aeration for up to 3 days without conditioning led to the best sludge dewaterability. The best results were obtained at 1.5 days aeration for the conditioning mode with polymer, which improved the dewaterability up to 4.5 times in the optimum polymer dosage. In this case, the polymer dosage decreased by 30% compared to the non-aerated conditioned sludge. It indicates the effect of digestion retention time on dewaterability. At the beginning of the process, the decomposition of cellular material improves the release of water from solid particles. Still, its continuation reduces the dewatering capability due to reduced particle size and conversion to colloidal materials.

In some part of Iran such Isfahan province some farmers tend to use the digested sludge as soil conditioner or fertilizer, and some of the mentioned sludge may content of pathogenic bacterial agents, such as Salmonella. The aim of the present study was therefore, to assess level of contamination by Salmonella products of which are used solely for agricultural purposes. Periodic sampling and counting of the level of Salmonella were according to the method presented by American Public Health Association (APHA) and the United State Environmental Protection Agency (EPA). The results showed that the average number of Salmonella in the digested sludge of waste water treatment plant number 1 and Shahinshar, based of the most probable number were 24 and 11 per 4g dried sludge solids, respectively, and were higher than the standard 3 per 4g of dried sludge solids. Hence none of these two plants satisfied U.S. Government Environmental Protection Agency, for use of the sludge in agricultural works. The results taking from statistical analyese using Pearson’s correlation coefficien showed that there was a meaningful relationship berween the percentage of reduction of stabilized sludge (organic materials) and Salmonella for plant number 1 (p=0.009 and r =0.9907) and Shahin-Shar digested sludge (p=0.001 and r =0.9885). These results suggest the greater reduction of the volatile solids correlates with larger reduction in the level of Salmonella.

One of the most important ways that conserve fossil fuels is the use of renewable resources. Biogas is one of the most important renewable resources. Biogas is created from anaerobic fermentation of livestock waste in a fermentation chamber. Biogas technology is an important from several aspects; First، the significant social impact of this technology in the field of environment and human health. Second، it can be fired using biogas generators for generate electricity and third، sludge biogas unit output، would be a rich fertilizer that can greatly increase the efficiency of agricultural products. This paper delivers a cost-benefit analysis of biogas-fired plants، from the perspective of the private sector and the public sector، of the dairy industry in Iran. The results of both analyzes indicate high economic efficiency in the different sizes of biogas-fired power plants in Iran dairy industry.

As there are some health and environmental concerns about wastewater, dewatered sludge, increase in green waste, and restricted legislation about burning them outdoors, environmental health engineers are investigating to find a simple, cost effective and efficient method. This is aimed to have healthy, safe and sustainable disposal of such materials. Co-composting of sludge and green waste is a newly developed process which can help us to achieve this goal. This study was to investigate the most suitable ratio of dewatered sludge to green waste from Chonibieh wastewater treatment plant in Ahvaz, Iran, and assess the feasibility of co-composting of this waste. So, dewatered sludge was composted with green waste as a bulking agent in three different ratios (1:1, 2:1, 3:1: green waste: dewatered sludge W:W). Then composting proceeded in pilot vessels (M1, M2, M3) for 23 days. The C/N ratio, the percentage of total nitrogen, phosphorus, total organic carbon, humidity and pH were tested in certain periods and compared with the national standards. This study showed that in M1, M2, M3 pilots, all parameters (except for total phosphorus) including C/N ratio, percentage of total nitrogen and total organic carbon, humidity, pH could meet class 1 national standard in Iran. Moreover, this compost product could meet the EPA microbial standards, class A. So, the product of this compost process is completely stabilized and could be used in agricultural lands.

Sewage of non-metallic and mineral industrials such as tile and ceramic contain a large amount of heavy metals and minerals which can cause problems such as contaminating underground water and polluting the environment. Thus, the present study was done to evaluate heavy metals concentration in the effluent and sludge of the tile factory in Birjand. In this descriptive analytical study, 36 samples were taken from six pools in June 2010 (18 samples from the effluent and 18 samples from the sludge). Analysis of the rate of the heavy metals in the samples was done on the basis of the procedures mentioned in 3010 Standard Method book. It was found that mean concentration of the heavy metals Zn, Cr, Cd, and Pb in the effluent samples was 0.135±0.235, 0.21±0.022, 0, and 0.064± 0.017 mg/l; respectively. These concentration levels were less than permissible standards of the Iranian Environmental Protection Agency (EPA). But, in sludge deposited on the bottom ponds, concentration of the heavy metals Zn, Cr, Cd, Pb was 3160±278.15, 1493.52±352.95, 22.18±17./55, and 1139.11±737.5 mg/kg; respectively. The concentrations of Cd and Zn were less than those in the American EPA Standards, but Pb and Cr concentrations were more than EPA Standards to permit the use of sludge in the land. It was revealed that in the effluent of tile and ceramic industries heavy metals concentrations are higher than the environmental standards, which requires more supervision and surveillance of the environmental agencies

The disintegration of excess sludge from activated sludge units for production of a carbon source in post-anoxic processes in order to remove nutrients from wastewater streams has been widely used in recent years. For this purpose, ultra-sonication is one of the most applicable methods for the disintegration of cell membranes to provide carbon the source from disruption of microorganisms. Such substances extracted from disintegrated sludge can be used as readily bio-degradable sources of carbon to be used by other microorganisms in following process units. The amount of power (P) per volume (V) applied to the samples in specific durations (t) as well as the concentration of sludge are the most dominant factors in the determination of the disintegration process. The main hypothesis of this research is that if the sonication of samples is intermittent during the total time of ultrasonic radiation, the defensive mechanism of cells will be weakened due to irregular forces applied to the cell membrane. This will lead to degradation of microorganisms at lower Specific Energy (Es) while the energy consumption in the whole process will be reduced accordingly. The effect of this parameter has been investigated through this research, whilst no research has been focused upon this issue earlier in previous studies.
In this research, samples of secondary sludge have been disintegrated at the frequency of 24 kHz while the applied power, time of sonication and sludge concentration were changed for each set of experiment. As an extra independent variable, intermittent sonication was altered from 0.3 to 0.9 second. The Degree of Disintegration (DD) was monitored as a dependent variable to evaluate the efficiency of the sludge disintegration process. The sludge for disintegration was sampled at the outlet of an anaerobic tank fed by a continuous stream of wastewater. Prior to the anaerobic phase, the sludge was aerated in an aerobic tank at a retention time of 12 hours. Raw wastewater with the average COD content of 358 mg/lit was daily supplied from a municipal wastewater treatment plant named Mahalati and located at north-east of Tehran, Iran. The type ultrasonic set was Sonotrode with a five mm diameter probe manufactured by FAPAN (Iran). The generated frequency and maximum power generated by the set were 24 kHz and 300 watts, respectively. The degree of disintegration has been calculated by the method introduced by Muller (2000) and one Molar NaOH was used to determine the total COD of the sludge. To separate the supernatant of the sludge from its solid contents, a centrifuge set (SDN- United Kingdom) was used along with and ultra-filtration by a 0.45-micron glass filter (CHMlab, Spain). For experiment design, a Response Surface Method and Central Composite Design were developed using Design Expert software. The power, sonication duration, the solid content of the sludge samples and intermittent sonication were independent variables and degree of disintegration was considered as dependent parameters. For standardizing the independent variables, Specific Energy (Es) was calculated at each stage. Determinations of COD and solid concentration were performed in accordance with Standard Methods for Water and Wastewater Experiments. For COD measurement, a colorimetric method was used by Hach DR 1900 (Germany) as Spectrophotometer.Discussion of Considering the aforementioned independent parameters, a relationship between these variables has been proposed as the formula no.1. The desirability of the model has been evaluated through ANNOVA variance analyzes for the proposed logarithmic model. The R2 parameter for this model was calculated as 0.9797.Formula no.1: Log10 (DDCOD) = -3.27179 +1.78725E-003× Watt +5.28686× Seq +0.16406× Time -0.098290× Density -3.82414× Seq^2 -8.14053E-003× Time^2Considering response surfaces generated by the software for interactions of parameters and their effects on DD, it was figured out that when the power increases, the DD rises up to the maximum of 38% too (under circumstances of this study). Moreover, decreasing sonication sequence from 1 to 0.6 second, leads to increasing the DD and afterward, this parameter decreases significantly when the sequence reaches 0.4 second. Emitted energy from the probe of the ultrasound generator produces little bubbles of water due to acoustic cavitation. When such bubbles collapse, some radicals such as OH., OOH. and H. are formed, which attack the cells in their vicinity. By increasing the power and sonication time, production of such bubbles increases and consequently, the efficiency of the disintegration process significantly improves. Additionally, in the higher concentration of sludge solid contents, a portion of applied energy to the aqueous systems transfers to the solids instead of making cavitation. In the other words, parts of the ultrasound waves are damped by the microorganisms’ body. As a result, the number of collisions between radicals and cells are declined, which leads to a decrease in the DD parameter. Hence the more sludge is concentrated the less sludge disintegration occurs.
In order to the comprehensive understanding of the interactive between the parameters, Specific Energy (Es) was calculated and a relationship between Es and intermittent sonication with the degree of disintegration has been developed as the formula no.2:Formula no.2: DDCOD = -0.30799 +8.59092E-006× Es +1.21280× Seq -1.00445×Seq^2The desirability of the model has been verified by ANNOVA analyzes with an R2=0.9633. According to the respond surface, increase in Es leads to higher efficiency of sludge disintegration, while reduction of sonication sequences from 1 to 0.5 second, affects the DD parameter in such a way that the maximum DD takes place in sequences between 0.6 to 0.7 second. In such circumstances, it can be argued that little bobbles of acoustic cavitation thoroughly dispersed in the sample during the sonication period. These bubbles cause breaking of sludge flocs at the first stage and collapsing of cell tissues in next step. If the radiation is continuous, the resistance of cell walls is strengthened because of the uniform collision of bubbles to biomass and its defensive mechanism toward external forces. Such conditions will lead to decrease in the degree of disintegration. On the other hand, if the bubbles are not produced in an extremely short period of time (a portion of a second), cell’s discipline of defensive mechanism will be devastated and accordingly, they will be more vulnerable to external forces. This will lead to higher values of sludge disintegration.
Another phenomenon that was observed in the experimental phase is that when the specific energy increases the optimum point for intermittent sonication approaches from 0.6 to 0.7 second. The reason is that in higher Es values, applied energy to the sludge is high enough to destroy cell tissue. Thus, as soon as sonication starts, the cell membrane disrupts and the theory of alteration in the defensive mechanism of microorganisms takes place in the smaller scale. Through a comprehensive literature review associated with ultrasonic sludge disintegration, it was found that no study puts its emphasis on intermittent sonication and its effects on microorganisms. While it is stated that precise microscopic survey is needed to understand the exact mechanism, which has not been performed in this research, macroscopic observations confirm that intermittent sonication can improve the efficiency of the disintegration process. Accordingly, a hypothesis of destructive resonance in cells’ structure due to the irregular emission of waves is proposed in this study, which should be verified with other extensive microscopic observations. Assuming this theory, when radiation of waves is cut off for a very short period of time, defensive mechanism of microorganisms suddenly interrupts and the cells show a less resistance against external forces. This will lead to disruption of cells in rather lower energy levels