The measurement of phosphate compounds is critical in the biological wastewater treatment process.
Endress + Hauser has recently introduced STIP Helios in-situ phosphate measurement system which is typically used for monitoring the dosing of precipitants and nutrients in wastewater, but is extendable for use in biochemical applications such as fermentation and even in lower phosphate concentration ranges like drinking water.
Apart from the existence of carbon and nitrogen compounds the controlled presence of phosphate compounds is important for the biological wastewater treatment since careful monitoring of the phosphate concentration can reduce the costs of the expensive chemicals.
Costly chemicals are added to the aeration basin to precipitate out the phosphate. If too much chemical is added, it is drawn off with the sludge and wasted. If too little is added, the effluent will have high phosphate content and attract fines from the authorities.
Accurate monitoring of the phosphate concentration can reduce the costs of running a wastewater treatment plant significantly.
The modular construction of the Endress + Hauser Helios phosphate monitoring buoy is a big benefit, especially with regard to maintenance. The low module of the buoy is the filtration cell which is also used for storage of filtered sample.
From here the clear measuring solution is transported up to the next level where all fluid mechanical components are stored. This system is designed as a continuous flow analysis with segregated fluid transportation which only needs one pump.
In the fluidic module the sample is treated with all the required reagents. The resulting colour complex is then photo-metrically detected in an optical cell with a monolitical set-up.
Two different wavelengths of light are used to compensate for matrix effects. In the next two upper-positioned modules there are the electronics of the analyser along with the compressor unit which is responsible for filling and discharging the filtration cell.
In the top level a carousel with five colour-coded storage bottles for reagents and a cleansing solution is placed. After lifting the cover of the buoy the individual chemical containers can be easily replaced.
The separation of sludge and solids is an important precondition for the analysis of phosphate. It ensures that the remaining solids do not increase the maximum threshold value which can be considered by the standard turbidity compensation and does not affect the optical measurement.
The sample is prepared by sucking the wastewater through special filtration mats with a nominal mesh size of approx 2µ. Auto cleansing procedures allow low maintenance requirements and a high durability.
The Helios operates in-situ, directly in the wastewater or activated sludge. The system has an integrated filtration system with automatic back wash by ejecting the filtrate from the previous measurement thus ensuring reliable effective filter cleaning and only requires maintenance every four weeks.
The self-sufficient photometer automatically cleans the sample chamber and cuvette and combining this with automated daily self-calibration makes the Helios a reliable in-situ photometer
The measuring of phosphate is based on the blue method. Here the development of a molybdato-phosphate-complex is used as a detection proof of the reaction and the colour is detected photo-metrically.
By using the sequence of filtration, reaction and subsequent measurement of the formed colour complex a time of no more than 6 minutes per measuring cycle can be achieved.
The consumption per cycle and per reagent is 25µl which leads to a total reagent requirement of maximum 12 ml per day. The construction of the storage tanks requires a refilling only every 4 to 6 weeks and can be done with a minimum of tools. In addition, the buoy can be disconnected and taken to the lab for maintenance or acid refilling.
This new STIP Helios phosphate buoy requires little maintenance and is user-friendly and at the same time provides reliable and accurate phosphate measurement for wastewater, biochemical, and drinking water applications.