The key module in the CCP Minder will be the ammonia analyzer. Elevated levels of ammonia indicate trouble in both lobster holding and aquaculture facilities. Also, excessive total ammonia can result in mortality to the higher organisms, especially when high pH levels favour dissolved ammonia gas, which is more toxic than the ammonium form.
High levels (> 1 mg/L) of ammonia in the seawater in lobster holding facilities indicate excessive lobster mortality. While small quantities of ammonia are produced as a by-product of lobster metabolism, larger quantities are produced through biodegradation of organic matter (e.g. decaying deceased lobsters).
High levels of ammonia in aquaculture facilities indicate problems with the bio-filter of some other malfunction or abnormal situation. In both cases, the cause must be identified and corrected to avoid additional mortality.
Safe levels of unionized ammonia for adult lobsters vary between 0.32 mg/l @ 20 °C and 0.51 mg/l @ 5 °C. A unionized ammonia level in excess of 5 ppm can have a harmful effect on lobsters in storage, resulting in increased mortality. This in turn, leads to increased ammonia, leading to increased mortality ... , creating a deadly spiral that can result in heavy losses, unless the ammonia is detected and remedial action is taken
Traditionally, ammonia monitoring in lobster holding facility seawater has involved manual on-site analysis of a regularly taken water sample, using a colorimetric method (eg: the Nessler spectral-photometric method).
Ammonium ion concentration may be measured with a number of wet-chemistry or instrumental methods.
Ammonium ion concentration in water is also measured with an ammonium ion-selective electrode (ISE). Inside the ammonium ISE is a reference electrode immersed in a solution of fixed ammonium ion concentration. This solution is separated from the sample by a polymer membrane containing a chemical compound that reacts, selectively, with ammonium ions. Ammonium ions on each side of the membrane equilibrate with the reactive compound at the inner and outer membrane surfaces. A result of the passing of ammonium ions across the membrane surface from the sample is a measurable electrical potential that varies with the concentration of ammonium ions in the sample. This potential is measured with an external reference electrode (which is not the same reference electrode immersed in the sealed solution), and then scaled to ammonium ion concentration (provided the ISE has been calibrated with ammonium ion calibration solutions).
All ammonium ion-selective electrodes suffer interference from other ions, especially sodium and potassium. Even though the sensor is most selective to ammonium, other ions, when found in high concentrations, can dominate the sensor response. For example, concentrations of 23 mg/l of potassium ion, 821 mg/l of sodium ion, or 4,340 mg/l of magnesium ion all “look like” about 1 mg/l-N of ammonium ion to an ammonium ISE.
Because of the sodium ion interference, the ISE ammonium sensor performs poorly in salt water. Significant interference is not likely to be encountered in water with conductivity below 1,000 µS, but in sea water, which contains over 10,000 mg/l of sodium ion, an ammonium sensor would read over 12 mg/l-N for ammonium concentration, even in the absence of ammonium, because of the sodium interference.
Flow injection (FI) analysis is a technique well suited to the requirements of automated, on-line industrial process analysis, since it possesses the required features of rapid analysis, robustness, simplicity, versatility and minimal capital and operating costs.
The CCP Minder will report unionized ammonia actually present in the seawater, corrected for temperature and pH. It will put the owner on guard to pH swings which could very quickly put unionized ammonia into dangerous levels.
The critical control points at which alarming occurs will be adjustable by the operator.