Page 65 - Industrial Plants

increased risk of effluent violations. On the
contrary low BOD loading rates are adopted
for municipal wastewater treatment, which
are much less concentrated than industrial
wastewaters, in order to meet low effluent
concentrations. Anyway, a too low BOD
loading rate may indicate underutilization of
treatment capacity.
Monitoring BOD loading rates helps operators
assess the system’s capacity and
performance. It guides decisions related to
process adjustments like water distribution,
recirculation, aeration, and allows evaluation
of overall treatment efficiency.
BOD loading rates vary based on influent
characteristics, flow rates, and treatment
plant design. Properly designed treatment
systems balance BOD loading rates with greater the flushing intensity required.
available microbial activity according to the Although many trickling filters have
specific fill media characteristics. hydraulically driven distributors, some
In fact each channel type and size is suited distributors are equipped with mechanical or
for different organic loading ranges. Larger other speed controls, as it is in this project.
channels and vertical fluted channels are As a result, speed-control distributors now
needed as BOD loading increases. often allow normal operational speeds
ranging from 4 to 10 minutes per revolution.
• The Hydraulic Loading Rate (HLR): More importantly, many speed-control
The hydraulic loading rate refers to the volume distributors allow specifying a regular (daily or
of wastewater applied to a treatment system weekly) “flushing” speed that may slow the
per unit of time per unit of horizontal area. It distributor to more than 60 minutes per
quantifies the flow rate of wastewater through revolution.
a specific treatment component and it is Another design topic is determining the
normally expressed in m3/m2/hour. number of arms in the top distribution system:
The HLR determines how much wastewater a reducing it results in higher flow from each
treatment system handles and it affects arm, thus increasing the local flushing force
the contact time between wastewater and brought by the percolating water. This is
treatment media (such as soil, filter beds, or useful because the oldest (and less active)
biological reactors), as well as the washing portion of the biological film detaches from
force applied to the fill media. the media surface and is flushed to the
From an operational point of view, high HLR bottom of the filter. Excessive biofilm
results in a smaller installation footprint and thickness can impair oxygen transfer and limit
provides strong flushing force to remove the overall treatment efficiency. This flushing
spoil film but may lead to inadequate procedure avoids the clogging phenomenon,
treatment due to insufficient contact time, which is accumulation of excess biomass or
resulting in poor effluent quality. suspended solids on the filter media surface,
On the contrary, low HLR provides longer resulting in loss of treatment and other
contact time for treatment and thus ensures problems.
higher treatment efficiency but it requires The specific flushing rate depends on the
larger installation footprint. filter design, media type and organic loading.
Treatment system designers consider HLR
during system sizing and layout because In conclusion, ENEXIO ITALY successfully
while systems mut be able to accommodate addressed the project requirements by
fluctuations, balancing HLR with treatment implementing the following strategies:
efficiency is crucial. 1. Careful Internal Stratigraphy Design:
• ENEXIO ITALY meticulously designed the
• The flushing factor internal structure of the filter.
Generally, the higher the organic loading, the • Higher thickness of the foil media were

IndustrIal Plants - May 2024
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