Automation in the operations lab: From cuvette test to GANIMEDE

Transcription

1 PRACTICE REPORT LABORATORY AUTOMATION GANIMEDE Automation in the operations lab: From cuvette test to GANIMEDE Water quality cards from the past 15 years clearly illustrate the impressive progress that has been made in the treatment of wastewater in municipalities and industry. As a result of tighter limiting values, much more analysis is being carried out. This is reinforced by continuous monitoring. At the same time, laboratory analysis has also expanded significantly, as measurements are taken at lots of sampling locations. To meet the changed needs of our customers, we have developed GANIMEDE - an automatic laboratory analyser that measures phosphorus and total nitrogen. In this report, two facilities describe their continuous measurement programs. Keywords Total nitrogen, TN b Total phosphorus Labortory automation Monitoring Minimum requirement Register of direct and indirect dischargers

2 2 LABORTORY AUTOMATION Monitoring of total nitrogen at the Magdeburg/Gerwisch sewage treatment plant by Renate Gruschka The Magdeburg/Gerwisch sewage treatment plant is designed for a population equivalent (PE) of 426,000. It serves the city of Magdeburg and surrounding communities, water and wastewater associations. The plant The biological treatment stage of the sewage treatment plant consists of a two-line activated sludge cascade. After passing through a digester and being mechanically dewatered, the sludge is used for agricultural purposes. Two cogeneration units convert the digester gas into electrical and thermal energy for the plant s own use. The task Just like other sewage treatment plants, we have to monitor our operations in conformity with the self-monitoring regulations of Saxony-Anhalt. The purpose of our extensive sampling and analysis is to safeguard the operational safety of the sewage treatment plant process by keeping the monitored values below the limiting values. Adequate control of the process is ensured by taking samples at defined locations (see Table M-1) on each work day and analysing them. The analysis The parameters analysed at sampling locations 1, 2, 4 and 5 are: ph, conductivity, settling solids, filterable solids, COD, BOD, TN b, NH 4 -N, NO 3 -, P tot, AOX, H 2 S, toxicity. The parameters analysed at sampling location 3 are: temperature, ph, acid capacity (Ks4.3), COD, NH 4 -N, NO 3 -N, NO 2 -N, P tot, TS, diluted slugde volume, sludge volume index (ISV), sludge activity. The samples are taken as qualified random samples at different times of day. In this way, a good distribution of the analysed samples is obtained over a period of a year. The significance of self-monitoring What conclusions can be drawn with the help of the above mentioned sampling and analysis program at the individual measurement locations? Sewage treatment plant inflow Representation of the capacity utilisation of the plant Sewage treatment plant inflow/ outflow Representation of the plant s degradation efficiency Inflow to biological treatment stage Optimal metering of turbid and centrate water. This enables the ammonium content to be controlled. Optimal adjustment of C:N:P ratio, acid capacity, ph Sampling location (no.) Name Parameters Analysis interval Additional parameters 1 Plant inflow TN b NH 4 -N, NO 3 - Each work day Chloride 2 Inflow to biological treatment stage TN b NH 4 -N, NO 3 - Each work day Acid capacity, organic acids 3 Outflow of the activated sludge cascade NH 4 -N, NO 3 -N, NO 2 -N Each work day Oxygen reading in aeration tank 4 Plant outflow TN b, NH 4 -N, NO 3 - Each work day Acid capacity, TOC, turbidity 5 Direct discharge to sewage treatment plant TN b NH 4 -N, NO 3 - Monthly, 2 dischargers per week Acid capacity Table M-1: Sampling locations and measurement parameters of the Magdeburg/Gerwisch sewage treatment plant 2001 Month January February March April May June July August September October November December Plant inflow N tot average value mg/l Plant outflow N tot average value mg/l Efficiency Plant inflow Plant outflow % N tot inorg N tot inorg average average value mg/l value mg/l Efficiency Table M-2: Efficiency of degradation of total nitrogen and total inorganic nitrogen in % Average value

3 3 Outflow of the activated sludge cascade Representation of nutrient elimination in the aeration tank, C, N, P Adequate acid capacity, ph Regulation of P tot (< 1 mg/l) with simultaneous FeCl 3 precipitation Plant outflow Monitoring of official limiting values Direct dischargers Introduced C, N, P loads Introduced pollutants and inhibitors, and their influence on biological sludge and sewage sludge Proportion of organic/inorganic nitrogen In view of the requirements of the 5 th amended wastewater ordinance with regard to the monitored parameters TN b and N tot inorg, we reviewed the scope and usefulness of our analysis of the nitrogen parameters. With the help of the parameter TN b, the nitrogen parameters TKN and N org can be calculated Month January February March April May June July August September October November December Year sum Year average Year min. Year max. Average mg/l Plant inflow TKN PE Freight kg Table M-3: Capacity utilisation of the sewage treatment plant in 2001 Evaluation options Efficiency of the sewage treatment plant in relation to TN b and N tot inorg (see Table M-2: ratio of inflow to outflow, 2001). Capacity utilisation of the plant (TKN - PE) (see Table M-3: Inflow 2001). The composition of the total nitrogen load from individual direct dischargers can be determined or calculated (see Fig. M-1 and M-2). Fig. M-1: Composition of the nitrogen components of discharger 1 Online and laboratory measurements complement each other. Together with the existing continuous measurement instruments, the extensive analysis program helps us to achieve our objective - optimal operational reliability - and to identify any disturbances at an early stage. In view of the large number of analyses that have to be performed, automatic laboratory analysers are an ideal extension. Fig. M-2: Composition of the nitrogen components of discharger 2 Portable or stationary samplers supply the samples for the laboratory. HACH LANGE

4 4 LABORATORY AUTOMATION Monitoring of total phosphorus at the Dresden-Kaditz sewage treatment plant by Petra Rötzsch In dry weather, the Dresden- Kaditz sewage treatment plant has a capacity of 115,000 m 3, corresponding to a PE of 650,000. The catchment area includes the city of Dresden and the neighbouring municipalities of Freital, Radebeul and Bannewitz. The plant The chemical treatment stage consists of a dispensing station for the purpose of phosphate elimination. The biological treatment stage consists of 20 aeration tanks and 20 final sedimentation tanks. The plant handles very large quantities of sewage and has no nitrification or denitrification stages. After mechanical dewatering and subsequent drying, the sludge is currently used in the agricultural sector and for rehabilitation after being composted and mixed with soil. The task The outflow of a properly functioning mechanical and biological sewage treatment plant contains considerable amounts and concentrations of inorganic plant nutrients, especially phosphate and nitrogen compounds. In order to comply with the minimum requirements of the Wastewater Act and the EU directive, these substances must be quantitatively analysed. The licence granted to the Dresden- Kaditz sewage treatment plant under the water laws prescribes a monitoring value of 2 mg/l for P tot until 31 December From 1 January 2005 this limit will be reduced to 1 mg/l, in line with the minimum requirement specified in Annex 1 of the Wastewater Ordinance. The wastewater that enters the plant passes through the following treatment stages (see Fig. D-1): 1 Inflow buildings P tot in inflow approx. 6 mg/l 2/3 Coarse and fine screens 4 Grit chamber 5 Pumping station 6 Pre-settling Chemical treatment stage: Chemical phosphate precipitation as simultaneous precipitation, efficiency of P elimination ~ 81% 7 Aeration tank 8 Final sedimentation tank Sludge treatment Outflow to the Elbe, P tot in outflow approx.1 mg/l The analysis There are measurement programs at each stage, which are implemented by our operations laboratory. Our team performs sampling and analyses in conformity with all quality requirements, using standard and, in some cases, our own methods. We strive continuously to make our laboratory analysis processes as effective as possible. Four measurement programs run currently at the above-mentioned stages. The following parameter are measured: ph COD BOD Ammonium, nitrate, nitrite and Kjeldahl nitrogen Orthophosphate Total phosphorus AOX Heavy metals There are two measurement stations in the inflow building. One is in the inflow on the Neustadt side and one on the Altstadt side. Some 1,380 indirect dischargers are currently listed in our indirect discharger register. No surges of phos- Return sludge Outflow Primary sludge Excess sludge FM = precipitation chemicals added Dewatered sludge Fig. D-1: Flow diagram of the Dresden-Kaditz sewage treatment plant

5 5 phate or nitrogen are to be expected from the majority of them. Samples are regularly taken from about 500 indirect dischargers. The loads in their discharges are diluted, so that the average concentration of total phosphorus in them is approx. 6 mg/l. The next measurement station is in the total inflow stream and in the inflow to the biological stage. Up to this point the total phosphorus content remains constant, as the wastewater has only been treated mechanically. Parallel to the measurement station in the total inflow is the discharge inflow point for process wastewater. As can be seen from the flow diagram (Fig. D-1: FM), phosphorus is precipitated with iron(iii) chloride sulphate downstream of the measurement station in the inflow to the biological stage. The amount added depends on the inflow amount and the PO 4 concentration at the aeration tanks 7 and 13. It is controlled with the help of online measurements. The operations laboratory carried out regular comparative measurements at the measurement stations of the aeration tanks 7 and 13. Deviations are immediately discussed with the operations personnel and any disturbances can be responded to immediately. The final measurement station is in the outflow to the Elbe. 24-h mixed samples are analysed for total phosphorus and other parameters here. An online measurement station for total phosphorus, orthophosphorus, etc. is also installed. Online measurements and comparative measurements are carried out here to enable out-of-control situations to be responded to. Using the available data, the sewage treatment plant can be operated in a stable manner. The operator can optimise the processes and thus directly influence the costs (e.g. through the power consumption of the blower or the amount of precipitant used) of the wastewater treatment. The significance of self-monitoring The self-monitoring tasks in the sewage treatment plant can be summarised as follows: Monitoring in conformity with the requirements of the self-monitoring ordinance of the Free State of Saxony and the conditions of the licence granted to the Dresden-Kaditz sewage treatment plant under the water laws. Advanced studies to facilitate transparent operation of the plant with the aim of ensuring that it functions properly and is run as efficiently as possible in terms of plant costs and performance. Provision of the necessary data for a balance sheet and assessment of the plant. The analysis of total phosphorus is defined in the German standard methods for the examination of water, wastewater and sludge, DIN EN 1189 D11/item 6. This method is time and labour-consuming, as many manual steps are involved before the analysis result is available. Moreover, the large number of steps increases the probability of errors. We therefore decided to test the GANIMEDE P analyser, which analyses total phosphorus automatically, in order to determine whether it provides comparable results to our usual analysis. An extensive series of studies of the equivalence of the two methods in conformity with DIN A 71, section e), f) was carried out in our operations laboratories: Sewage treatment plant method: DIN EN 1189 Digestion of the original sample with peroxodisulphate LANGE method; Determination by means of an automated procedure in conformity with DIN EN 1189 Measurement of 15 samples from the sewage treatment plant inflow using both methods Measurement of 15 samples from the sewage treatment plant outflow using both methods The measurements demonstrated the equivalence. Measurement of a 2.0 mg/l standard solution with both methods There were slight deviations in these measurements, which could not be The convenient control unit enabled the measurement results to be transferred cordlessly to a PC. The ready-to-use reagents are a major advantage, as they save time and eliminate errors. HACH LANGE

6 NITROGEN_COMPARABILITY Summary reproduced as there was a shortage of analysis solutions. The calibration function and the analytical limiting value as referred to in DIN were determined Result We found that we could work more effectively with the GANIMEDE P analyser and the associated analysis. Equivalence in conformity with DIN A 71 is ensured. We have the option of newly configuring the organisational procedures in the laboratory. The potential time savings are clear from the case of, for example, 12 analysis samples (single determination; double determination only for unknown samples). About one hour less time is required. The analysis results for about 12 samples are available after one hour, whereas, if the DIN method is used, they are first available after two hours. Conclusion In order to comply with the increasingly stringent legal requirements concerning the treatment of wastewater, it is necessary to determine a number of parameters, one of which is total phosphorus (P tot ). Regular self-monitoring has to be carried to ensure that limiting values are not exceeded. The LANGE GANIMEDE P enables reliable results to be obtained quickly. Alternatively, this instrument can also be used to analyse orthophosphate. This is an additional safety factor for our laboratory, in terms of redundancy. Outlook By the end of 2004 the Dresden-Kaditz sewage treatment plant will have a nitrification and denitrification stage. For this purpose, new aeration tanks with a total volume of about 110,000 m 3 and six new final sedimentation tanks will be installed. This extension will ensure complete nitrification and, in the majority of cases, adequate denitrification. Subsequently the final sedimentation tanks of the current sewage treatment plant will be converted into an additional upstream denitrification stage and the current aeration tanks will become an anaerobic preliminary stage of the biological phosphorus elimination process. From 2006 the wastewater from the neighbouring towns of Pirna and Heidenau will also be treated in this plant. This will increase the number of connections to a population equivalent of 740,000 PE and the average volume of incoming wastewater to about 130,000 m 3 /d (dry weather value). The HACH LANGE Services Contact us to place an order, request information or receive technical support. Support on-site by expert sales team. Quality assurance complete with standard solutions, instrument checks and test solutions. - up-to-date and secure, with downloads, information and shop. Extended warranty with inspection contract. Regular customer information by post and . DOC Jun04