The ammonia recovery system is a wastewater treatment process equipment fitted into two maritime containers. The designs, PID, equipment lists, control description and automation description have been prepared by Ramboll Finland. This project is for the construction of the Demo unit.
Overview:
The nitrogen recovery system is designed to remove nitrogen from wastewater and store it in a product recovery tank for further processing to dried form. The system consists of a series of membrane modules that operate in the presence of acid to separate nitrogen from water. The acid is recirculated through an acid-active tank to capture the separated nitrogen. A concentrated acid tank provides fresh acid when acid in circulation has been exhausted. The wastewater is fed from a feed tank and undergoes pH correction by lime or sodium hydroxide dosing systems before entering the membrane feed system. The product recovery system collects the nitrogen-rich stream from the membrane modules and transfers it to a product recovery tank. The acid refill system replenishes the acid in the concentrated acid tank when the pH changes to a set point.
Process description:
Nitrogen Nutrient Recovery
The nitrogen nutrient recovery process is designed to recover ammonia from the wastewater using membrane separation technology. The system configuration is provided in Table 1, Plant Configuration. The wastewater is fed to the wastewater feed tank (P2-TNK01) via inlet flow control valve P2-HV02 through a direct connection from the wastewater pumping network or the bottom of the wastewater buffer tank from the client premises. If the source of wastewater is from an underground tank, ditch, or some sewer channel, then the same can be pumped via feed pump P2-CP01. The tank P2-TNK01 is equipped with a level controller and level switches, which help in maintaining the level of wastewater in the tank. The tank also has a turbidity analyzer and an ammonia analyzer. The wastewater from the feed tank P2-TNK01 is transferred to the membrane recovery system via pump P2-CP02 and flow control valve P2-HV01. The pH of the wastewater is adjusted by dosing lime or NaOH in a static mixer, which is fixed on the discharge line of the membrane feed pump P2-CP02. The Lime dosing system consists of a dosing tank P4-TNK02, which stores the Lime. The capacity is sufficient for one week of chemical requirement. The Lime is dosed in the wastewater line based on the pH of the wastewater via dosing pumps P4-KP02A/B. The dosing rate can be adjusted by changing the frequency on the variable frequency drive (VFD) installed on the dosing pump. Similarly, the pH can be adjusted by dosing lime solution in the wastewater. The lime dosing system consists of a lime storage silo P24-K01, a lime conveyor system P4-K02, a lime slurry preparation and storage tank P4-TNK01, which has a mixer P4-SK01 installed for slurry preparation, and lime dosing pumps P4-KP01A/B. The pH can be adjusted by either of the chemicals based on the operator 's choice.
The wastewater is fed to the membrane modules, which consist of four trains MB06 to MB010, each having five sets of membrane modules. The wastewater is fed to the membrane modules via a set of solenoid valves, which help in series and parallel flow configuration and bypass specific modules. Each of the membrane modules has a wastewater inlet and outlet, where the wastewater flows by the hollow membrane fibers in the module (wastewater is outside the membrane fiber).
The solenoid valves P2-SV01 to P2-SV069 are used to control the flow of wastewater to each module and to bypass any module that is not in operation. The solenoid valves are operated by the programmable logic controller (PLC) based on the operator 's input. The membrane modules also have an acid inlet and outlet, where a up to 98% sulfuric acid solution is circulated to extract the ammonia from the wastewater. The acid solution flows through the inside of the membranes. Ammonia that passes through the membrane fiber wall reacts with the acid inside the fiber, forming an ammonia salt. This means that ammonia concentration is zero inside the fiber. This creates a concentration (partial pressure) gradient that drives the ammonia transfer across the membrane pores.
The pressure-reducing valves P3-PRV-01 to P3-PRV20 are installed on the acid inlets of each module to prevent pressure buildup inside the membrane fibers as too high pressure would lead to membrane rupturing. The acid recirculation process is repeated until the acid solution reaches a certain pH level, indicating that the available acid in the circulation has been exhausted and has captured as much ammonia as it can. The acid active tank is equipped with a pH sensor and a level sensor, which monitor the pH and the volume of the acid solution. When the pH sensor detects that the pH of the acid solution has increased to a preset value, the PLC stops the acid recirculation process and initiates the ammonium salt transf