Hidrológiai Közlöny 2006 (86. évfolyam)

3. szám - Kaposvári Kázmér: Description of the Szolnok municipal waste water treatmant plant based on the operation experiences of the 2000–2004 period

J^POSVÁR%H|^^escri£tk^ 31 facility which is the sludge fermentation hall, together with the sludge dewatering machinery shop. The completely enclosed hall has approximately 1300 m floor area and 5 m internal height. The dcwatered sludge which is the byproduct of the biological waste water treatment is removed from the centrifuges by a screw feeder and transferred to the sludge receiving area of the fermentation hall. Presently chopped crop straw is used for the sludge composting as C source. The crop straw shall provide: - the sufficient dry substance content of the mixture (a 40^60 % moisture content mixture is produced from the dewatered sludge having 20^23 % dry substance content), - the proper C/N proportion of the mixture, - the good ventilation and structure of the mixture. The sludge and the straw have completely different specific densities, therefore the mixing of these materials requires great attendance and extensive experience. If the mixing is not done in a professional way, then the resulting mixture will not be homogeneous or becomes adobe shaped which is not suitable for quick composting. The volumetric ratio of the dewatered sludge and the chopped straw is 1 :(2-K3) depending on the actual water contents of the sludge and the straw. The mixed material is transferred to the conditioning basin by a conveyor. This stage is required in order to provide the continuous, uninterrupted fill up of the fermentation chamber. The most important unit of the plant is the fermentation chambcr. When approx. 70-90 m

3 substance, i.e. a sufficient amount for one chamber has been collected, the front loader fills up one of the 35 irf

, thermally insulated RCC chamber in 2.0-2.5 m height. The five chambers are located next to each other along one of the lengthwise side of the hall. The internal side of the chamber is closed by a thermally insulated door. When the chamber has been filled up, the doors are closed and the automatic, computer controlled ventilation is turned on. The air (oxygen) injection is provided through the air conduits and the perforated plates located on the floor level. The water vapor and the gases produced by the process are extracted by the fans built into the back, i.e. the outer wall of the chambers. The collected gases are directed to the activated sludge basin by the blowers, where the substances causing the smelliness become absorbed by the high volume and good absorbent activated sludge. The monitoring and control of the chamber temperature is provided by programmable multipoint temperature sensors. These sensors record the variation of the substance temperature in the chamber and submit the data to the central computer to maintain the required level. The emptying of the chamber can be started when the temperature of the mixture has been successfully maintained above 65 C for at least 72 hours. The unloading is also done by the front loaders. The material is loaded onto tipping trucks entering into the hall. They transport the compost to the temporary storage before the utilization. The fresh sludge compost is an important land conditioner and yield improving end product and its parameters must be known before utilization. For example, how it affects the processes and the parameters in the soil, how it contributes to the maintenance of the nutritive reserves and how the contaminants of the sludge create extra load in the soils. In the Szolnok plant around 8000 to/year compost is being produced by composting the waste water sludge which amount is completely used in the agriculture. The composted sludge became a qualified product in 2003. The qualification was done by the Ministry of Agricultural and Country Development and the product name is SZOLKOMP. Evaluation of the emission parameters of the waste water treatment plant on the basis of data from the 2000-2004 period Upstream the waste water affected Tisza section, the water quality of the river varied between class II and IV in the observation period according to the classification contained in MSZ 12749:1993. Hungarian Standard (Table I). Table 1: Water quality of Tisza river at the Szolnok section (334,20 rkm) 2000 2001 2002 2003 2004 Oxygen balance 111. III III. in. III. Nutrition household III. III. II. ii. II. Microbiological parameters III. 111. 111. ii. ill. Organic and non-organic micro contaminants IV. IV. IV. IV. III. Other parameters II. II. II. II. II. The average volume of the waste water received by the treatment plant increased from 20589 m

3/d to 25620 m

3/d between 2000-2004. A comparison was made between the received water quality data and published values (see Table 2) - (Gray 1999; Öllős 1994). It can be concluded that the water coming to the Szolnok plant shows average quality parameters. The yearly average values of all the six parameters monitored by us, varied between the limits published in the mentioned paper. Table 2: Quality parameters of the raw waste water received by the Szolnok treatment plant pH COD BODS NH

4

+N total P Sus. solids (mp/1) (mp/l) (mp/l) (mp/l) (mg/1) Maximum 8 3729 460 78 6.2 1144 o o Minimum 6.9 226 80 10.8 1.3 36 Average 7.6 615.2 245.8 40.3 4.1 313.4 Maximum 8.1 726 660 83.5 11.3 900 ® o Minimum 7.2 236 60 17 0.1 14 Average 7.7 391.5 224.2 38.8 4.4 204.9 Maximum 8 780 950 52 21.6 2524 o o Minimum 6.9 164 80 6.5 0.2 22 Average 7.6 489.8 266.4 36.5 5.9 373.6 Maximum 8.5 2756 660 56 13.9 602 o o Minimum 7 248 160 20.2 0.1 52 Average 7.5 580.3 323.8 37.9 6.6 244.4 Maximum 8 940 900 69.5 11.6 1736 o o Minimum 7 326 120 26 1.1 34 Average 7.6 569.6 318.1 42.0 7.0 539.4 In Table 2 the yearly maximum and minimum concentrations are also presented besides the yearly average figures. On the basis of the test results it can be concluded that the highest concentration variations can be identified in case of the chemical oxygen demand, the biochemical oxygen demand and the suspended components. The remarkable quality variation can probably be related to the high fluctuation of the waste water flow due to infiltration and rainfall. The waste water collection system of the Szolnok treatment plant is a partially combined type system. The extremely low concentration figures for the suspended components are also related to the high diluting volumes of the rainfall reaching the network.