PAEROA WASTE WATER TREATMENT PLANT 

The new Paeroa sewage treatment and disposal system was commissioned in January 2002.

All the Paeroa sewage including wet weather flows is collected at a new pumping station in Junction Road and pumped via a new pipeline to the new treatment site at Irwin Road. After treatment to remove contaminants, the cleansed water is discharged via a pipeline and rock diffuser to the Waihou River.

The treatment plant utilises of the following processes operating in series. 

Inlet		Aerated		Aerated		Retention		Gravel		UV Light
screen		pond (No 1)		pond (No 2)		pond (No 3)		filter		disinfection

PROCESS DESIGN 

The treatment process consists of three aerated lagoons in series, to provide the initial breakdown of organic material.  Aerators in the first lagoon are sized to provide the oxygen for BOD (Biological Oxygen Demand) reduction and for some nitrification. 

In the second and third lagoons, the aerators provide additional oxygen and also provide an ability to break up scums that may form particularly in the event of a blue-green algae bloom. 

The gravel filter beds provide an effective means of removing remaining BOD and suspended solids from the lagoon effluent.  These are removed by the filtering action on the stone and by biological processes within the microbial films growing on the stone. 

The design includes the provision for recirculation by one of the twin pumps in the outfall pump station to improve the potential for ammonia removal by recirculating flows back to the third lagoon via a nitrifying trickling gravel bed. 

The slag used in the gravel filter beds is expected to provide phosphorous removed by absorption for about six years. 

The UV disinfection plant will reduce indicator organism numbers.   It is not expected to significantly affect any of the other chemical or physical parameters of the treated effluent.