TSS removal

Introduction

TSS stands for Total Suspended Solids. TSS are the solid particles that are suspended in wastewater that do not settle out. In wastewater, TSS are mostly organic in nature and can serve as refuges for harmful bacteria and other microorganisms. TSS can limit sunlight from reaching aquatic plant life which is essential for photosynthesis, a natural process essential to life. TSS is difficult to settle out and remove. Like TP, TSS removal requires in some case high energy process to remove, extremly costly. PNW systems propose a cost-efficeint way to lower your TSS level.

Problem

TSS concentrations, in typical license requirements for lagoon effluent, range from 20 to 45 mg/l. The primary reasons for existing ponds exceeding allowable concentrations are:

Excessive algae growth in shallow aerated (<3.0 m deep) and unaerated high retention shallow wastewater stabilization ponds (no supplementary aeration)
Failing aeration systems (existing aerated lagoons)
Inadequate hydraulic retention time (HRT) for solids solubolization and final settling.

Inadequate HRT in existing ponds is typically a result of flows exceeding the original design or because of excessive sludge accumulation.

Solution

PNW engineered lagoon system are built with three main components : Aeration, Biofiltration and Bioaugmentation. ADS fine bubble diffusers are placed on the bottom of the cells perpendicular to the flow of the wastewater. Convection cells are created between the diffusers, direct result of the rise of the bubbles and subsequent mixing. By rising with a slow laminar flow of water, the solids settle out through the downward motion of the water between the diffuser lines where the circulation loop is completed. Additional suspended solids removal is facilitated by a slower mixing rate in the secondary cells where turbulence are reduce.

Continual oxygen addition provided through the bottom laid diffusers assure a high biodegradation rate of the solids reaching the bottom of the lagoon. This process results in minimal organic bottom sludge accumulation. The environmental impact and cost of sludge removal and disposal can be minimized utilizing ADS aeration.

The algae formation is significantly reduced by the grid mixing repartition compared to the conventional passive wastewater stabilization lagoons. Lower algae production results in lower suspended solids in the lagoon effluent. By introducing oxygen into the system, nutrients are provided to microorganisms instead of algae. The use of Bacta-Pur® bacterial augmentation and AquaMats® high surface area biofiltration curtains in conjunction with ADS aeration further reduces algae concentrations.

For improved results of the installation, ADS aeration can be used in final settling ponds without compromising solids removal. Aerating the settling pond produces effluent with high dissolved oxygen and prevents the pond from going anaerobic.

You do not need to dewater or interrupt lagoon service to upgrade a failing existing aeration systems resulting in inadequate oxygen transfer and mixing. PNW propose a simple procedure for the installetion. With various aeration technologies and air header options upgrading complex lagoon configurations are attainable.

Performance

In a PNW municipal wastewater lagoon, typical TSS removal efficiencies are 84 to 93% with 15 to 35 mg/l effluent concentrations.