Struvite recovery and phosphorus management techniques for wastewater treatment plants

A waste treatment process comprising:

• processing waste activated sludge (WAS) in a thermophilic digester to produce a thermophilic digestate;
• increasing pH of the thermophilic digestate with an air stripper/heat exchanger subsequent to the thermophilic digester;
• forming struvite in the air stripper/heat exchanger to reduce a limiting element of struvite formation from the thermophilic digestate, thereby reducing struvite scaling on downstream equipment;
• cooling the thermophilic digestate concurrently with increasing pH of the thermophilic digestate in the air stripper/heat exchanger;
• producing from the thermophilic digestate that has been increased in pH and cooled, a treated digestate containing struvite with a struvite reactor;
• separating struvite from the treated digestate,
• subsequent to separating struvite from the treated digestate, processing the treated digestate in a mesophilic digester to produce a mesophilic digestate;
• and
• dewatering the mesophilic digestate to produce effluent and solids.

A waste treatment system comprising:

• a thermophilic digester that produces a thermophilic digestate from waste activated sludge;
• an air stripper/heat exchanger, downstream of the thermophilic digester, that is fed a thermophilic digestate from the thermophilic digester and concurrently removes carbon dioxide from the thermophilic digestate to increase pH of the thermophilic digestate to reduce struvite scaling on downstream equipment and cools the thermophilic digestate by heat transfer from thermophilic digester to the waste activated sludge;
• a mesophilic digester, downstream of the air stripper/heat exchanger, that produces a mesophilic digestate from pH increased and cooled thermophilic digestate;
• a struvite reactor that produces a treated digestate containing struvite from the mesophilic digestate;
• and
• a pump downstream from the struvite reactor that supplies the mesophilic digestate to a cyclone separator to separate struvite from the mesophilic digestate.

A waste treatment process comprising:

• supplying waste activated sludge through a heat exchanger to a thermophilic digester;
• processing the waste activated sludge received from the heat exchanger in a thermophilic digester to produce a thermophilic digestate;
• increasing pH of the thermophilic digestate downstream of the thermophilic digester prior to any other processing;
• forming struvite concurrently with increasing pH of the thermophilic digestate to reduce a limiting element of struvite formation from the thermophilic digestate and to reduce struvite scaling on downstream equipment;
• subsequent to increasing pH of the thermophilic digestate and prior to any other processing, cooling the thermophilic digestate in the heat exchanger by heat transfer from the thermophilic digestate to the waste activated sludge;
• processing the pH increased and cooled thermophilic digestate in a mesophilic digester downstream of the heat exchanger and prior to any other processing to produce a mesophilic digestate;
• producing, with a struvite reactor, a treated digestate containing struvite;
• and
• separating struvite from the treated digestate with a cyclone supplied by a pump.