Wastewater Treatment Lagoons

  

Lagoons are pond-like bodies of water or basins designed to receive, hold, and treat wastewater for a predetermined period of time.  In the lagoon, wastewater is treated through a combination of physical, biological, and chemical processes.  Much of the treatment occurs naturally, but some systems use aeration devices to add oxygen to the wastewater.  Lagoons can be classified as anaerobic, aerobic, and facultative.  Anearobic means “without oxygen”.  Aerobic means “with oxygen”, and facultative means both with oxygen and without oxygen.  Inside an anaerobic lagoon solids in the wastewater separate and settle into layers.  Odor can be a problem with anaerobic lagoons.  However, in many cases odor can be managed through a variety of methods such as adding sodium nitrate, recirculating pond effluent, and through regular maintenance.  An aerobic lagoon utilizes aerators to mix the contents of the system and add oxygen to the wastewater.  They are sometimes referred to as partial-mix or complete-mix lagoons depending on the extent of the aeration.  Partial-mix aerated lagoons are often anaerobic lagoons that have been adapted and upgraded to receive more wastewater. 

  

  

Like most natural environments, conditions inside a facultative lagoon are always changing.  Lagoons experience cycles due to variations in weather, the composition of the wastewater, and other factors.  In general, the wastewater in the facultative lagoons settles into three fairly distinct layers or zones.  Different conditions exist in each zone, and wastewater treatment takes place in all three.  The top layer is called the aerobic zone, because the majority of the oxygen is present there.  The wastewater in this part of the lagoon receives oxygen from the air, mechanical agitation of the surface, and natural of the water surface.  This zone also serves as a barrier for the odores from gases produced by the treatment processes in the lower layers.  The anaerobic zone is the layer at the very bottom of the  lagoon where no oxygen is present.  This area includes a layer of sludge which forms from the solids that settle out of the wastewater.  Here, wastewater is treated by anaerobic bacteria, microorganisms such as protozoa, and sludge worms, all of which thrive in aerobic conditions.

  

Names for the middle layer include the facultative, intermediate, or aerobic-anaerobic zone.  Both aerobic and anaerobic conditions exist in the layer in varying degrees.  Depending on the specific conditions in any given part of this zone, different types of bacteria and other organisms are present that contribute to wastewater treatment. 

  

  

Bacteria treat wastewater by converting it into other substances.  Aerobic bacteria convert wastes into carbon dioxide, ammonia, and phosphates which, in turn, are used by the algae as food.  Anearobic bacteria convert substances in the wastewater to gases such as the odorous (rotton egg) hydrogen sulfide, ammonia, and methane.  Many of these by-products are then used as food by both aerobic bacteria and algae in the layer above.  In addition, the sludge layer at the bottom is full of anaerobic bacteria, sludge worms, and other organisms which provide treatment through digestion and prevent the sludge from quickly accumulating to the point where is needs to be removed.   

  

  

Weed and long grass-Banks need to be mowed and weeded regularly

  

Blue-green algae-Unlike green algae, this alga is stringy and can clump, block sunlight, and cause short circuiting.  It can dominate lagoons when conditions are poor, when pH is low, or when protozoa eat all of the green algae. 

  

Algae blooms-After periods of cloudy weather or abrupt temperature changes, algae multiply quickly and then die off.  Matted algae on the surface can block sunlight and cause foul odors.

  

Odors-Lagoons may have odors occasionally from algae blooms, anaerobic conditions, scum, and turnover of the lagoon after thawing.

  

Short-Circuiting-“Dead spots” in the flow pattern, due to obstructions in the lagoon or to wind on the surface, can cause wastewater to leave the lagoon too quickly.

  

Sludge accumulation-Sludge in the bottom of lagoons should be measured at least once per year and removed if necessary. 

  

  

Application of liquid hydrogen peroxide (H2O2) is becoming very common in wastewater lagoon systems for the purpose of providing an immediate increase in dissolved oxygen and a consequential reduction of BOD (biological oxygen demand).  The need for a supply of supplemental dissolved oxygen typically occurs when biological treatment systems such as lagoons experience temporary overloads or equipment failure.  The increase in dissolved oxygen due to hydrogen peroxide addition also helps to serve in reducing “nuisance odors” that can occasionally be found during lagoon operations.

  

  

Typically, remedies for lagoon problems are a fairly simple process.  In most cases, the lagoon system is either experiencing an increased load  and unable to supply sufficient oxygen or its undergoing a seasonal “turnover” which will release odorous gases and temporarily upset the bacterial process.  We have seen significant improvements in lagoon operation while using any number of the following WLFT additives:

  

WLFT #426 Nitraid:  Lagoon odor control-bacterial stimulant and nitrate booster to eliminate hydrogen sulfide gas production.

  

WLFT # 220 Blue Bacteria:  Sewer lines-loosens and liquifies heavy grease deposits in lift stations and grease traps.

  

WLFT # 220 Red Bacteria:  Grease traps-helps reduce the amount of fats, oils and greases (FOGs) in lift stations and waste streams.

  

WLFT Bio D 220 Bacteria:  Lagoon performance-micronutrient supplement designed to sustain and develop a healthy biological population in the lagoon system.  Available in liquid form (BIO-L220) or granular form (BIO-D220).

  

WLFT H2O2 Hydrogen Peroxide:  Supplemental oxygen provider; liquid added directly to the waste stream or distributed throughout the lagoon.