In managed closed environments, typical of the average pond, the problem of excess ammonia, nitrites and nitrates becomes apparent. The volumes of water in a fish pond are quite minute when compared to a large lake so there is far less dilution nitrogenous compounds.

Ammonia is constantly being produced in aquaculture environments, small amounts can be traced to the diffusion of blood across the gill membranes of fish, but the majority of ammonia is produced through the process of mineralization which involves the conversion of waste products in the pond to ammonia by heterotrophic bacteria.

Another difference is the lack of plant life in the average pond. Algae, which produces 'green water', and blanketweed are actively discouraged by fish keepers, leading to very little nitrogen being converted into plant protein. The end result is that free nitrogenous compounds are common in fish ponds - in stark contrast to what one finds in nature.

Symptoms high ammonia, nitrite and/or nitrate

low oxygen levels
excessive green water or filamentous algae
excessive sludge
poor flavor of fish due to poor water quality
fish stressed
many diseases
poor conversion efficiency excessive nitrogen and phosphorus in effluent.

Extremely expensive (capital and operating) mechanical treatment plants have replaced many lagoon systems to facilitate ammonia removal.

Construction of mechanical treatment plants is not economically feasible for most small to medium sized communities. Since most of the communities have existing lagoon infrastructure, the ability to upgrade the lagoons for enhanced ammonia reduction is not only more cost effective, but promotes maximum utilization of existing infrastructure.

Solution

Three major factors can be modified to ensure that ammonia removal continues in cold weather conditions (water temperatures below 5°C): dissolved oxygen, surface area, and beneficial bacteria. PNW propose combinatinated technolgies such as aerated or stabilization pond system upgrades to facilitate ammonia removal.

High level of Dissolved Oxygen with ADS

Aerobic conditions are required for nitrifying bacteria. In order for the process to occur, a minimum dissolved oxygen (D.O.) concentration of 2 mg/l is necessary. If the dissolved oxygen levels are reduced to 0 mg/l (anaerobic conditions), the growth of all nitrifying bacteria is stoped. It's why in unaerated facultative lagoons, nitrification cannot occur in ice covered and winter conditions. ADS fine bubble aeration systems are cost effective ways of retrofitting existing lagoons (no dewatering required for installation) for the purpose of increasing dissolved oxygen levels throughout the year, including ice covered conditions. The aeration system should have the ability to maintain 3 to 5 mg/l at the final lagoon discharge to provide buffering for any variations in oxygen demand although nitrification can occur with D.O. concentrations down to 2 mg/l. ADS can easely maintain 3 to 5 mg/l of dissolved oxygen at the lagoon discharge point.

Large Available Surface Area with AquaMats®

In order to grow, bacteria require a medium of some form. High-density bacteria populations require and give the best result with high surface area medium. The creation of the surface area necessary for growth of the bacterial and algal colonies that facilitate ammonia reduction is provided by AquaMats® biofiltration curtain technology.

Large Populations of Nitrifying Bacteria with Bacta-Pur®

Two strains of bacteria, Nitrosomonas and Nitrobacter are responsible of the convertion of ammonia (NH3) to nitrite (NO2-) and ultimately nitrate (NO3-) (nitrification).

The appropriate strains of bacteria must be present to make full use of the increased oxygen levels and large surface area and assure high ammonia reduction. Increasing the populations in a controlled fashion improves the ammonia reductions although these bacteria are already present in the wastewater.

Increasing the concentrations of nitrifying bacteria populations to compensate for the reduced bioactivity in cold water temperatures is assured by adding Bacta-Pur® biological technology supplements.

Results

Depending of the location, temperature and hydraulic retention times influence ammonia removal. The discharge ammonia concentrations would range from 10 mg/l to less than 3 mg/l with a typical influent ammonia levels of 25 mg/l in municipal wastewater, assuming a minimum 35-day retention time in a 3 cell or 45-day retention time in a 2 cell aerated lagoon system.