The most efficient waste water sludge treatment

Struvite, silt and sludges from anaerobic digesters have typically been a major problem to wastewater treatment plants, due to the low flow rates achieved with centrifuges and long downtime of the digesters when they required cleaning. Flowmax solves this problem with its high throughput and dry solids (40-60% from a highly variable feed of 2-25%). This presents a marked improvement over centrifuge solutions.

In its simplest form, the sludge/slurry treatment process has three stages:

Stage 1: Adding Flocculants

Wastewater sludge has two types of contaminants; particles that are suspended in the liquid; and soluble chemicals that are dissolved in the liquid.

Flocculants are agents which cause dissolved chemicals to come out of solution or existing solid sludge particles to band together and form suspended particle clusters called ‘flocs’. These flocs can then be filtered in the same manner as other suspended particles.

Stage 2: Dewatering

Dewatering is the mechanical stage of the sludge treatment process where the solids and liquid are separated. While there are a large number of industries using ‘dewatering’ technologies, there are only a small number of actual technologies being utilised. The most common examples for waste water sludge treatment are:

Settlement Ponds
Belt Filter Press (BFP)
Plate-and-Frame Filter Presses
Centrifuge
Vacuum Belt Filter
Horizontal Gravity Belt Filters

No simple method exists for selecting the best dewatering process for a wastewater treatment plant. The dewatering process chosen will be a function of sludge disposal and capacity, along with the plant’s operation and maintenance capacities.

Stage 3: Cleaning the Filtrate and Drying the Cake

By this stage there are two outputs from the dewatering process:

OUTPUT 1 – While filtrate (liquid) coming out of the dewatering process may be ‘clear’, this does not necessarily mean it is ‘clean’. So depending on the intended use for the filtrate, there may be a need to clean it before returning it into an industrial process or discharging into the environment.

OUTPUT 2 – The cake (solid material) will still have a small percentage of liquid in it after the dewatering process is complete. If the cake is to be discarded into landfill or used as an organic agent, the process usually ends at this stage.

However, some applications such as energy generation will require that the cake go through an additional ‘drying’ process before being used.

At Watercare’s Mangere wastewater treatment plant in South Auckland, the struvite, silt and sludges from anaerobic digesters had been a major problem due to the low flow rates achieved with centrifuges, and long downtime of the digesters when they required cleaning.

The installation of Flowmax solved this problem for Watercare with its high throughput and dry solids (40-60% from a highly variable feed of 2-25%). For this company, Flowmax delivered a marked improvement over their traditional centrifuge solution, resulting in clear filtrate.