Algae
Organic wastewater contains large amounts of nutrients, which promote plant growth. After all, that's what makes the composted product so valuable as a fertilizer. During wastewater processing, plentiful nitrogen and phosphorus, often combined with relatively motionless water, support algae growth.
Algae isn't strictly a plant, although it does use photosynthesis. It's related to seaweed, that foamy green pond scum, and the single-celled free-floating algae that turn pond water green. The term algae also typically encompasses other non-plant photosynthesizing organisms such as cyanobacteria. Some forms of cyanobacteria produce the most potent natural toxins known to man and are responsible for many deadly algae blooms in ponds, reservoirs, waterways, and marine environments.
The link between wastewater, algae growth and algae blooms underscores the need to prevent the escape of untreated or under-treated sewage into the environment. Still, its presence causes more significant problems in the treatment process itself. Algae release oxygen during the day as it photosynthesizes but then consumes it at night. When algae are present in sufficient concentrations, depletion of oxygen overnight can kill beneficial aerobic bacteria populations. Once algae die, they add even more waste and nutrients, which must be removed during treatment. If this cycle continues without modification, the treated water will not meet effluent standards.
In "pristine" aquatic systems, nitrogen is usually the scarcest nutrient. Some forms of algae, however, can fix nitrogen directly from the air itself. With that advantage, it's hard for any other organism to outcompete an established algae mass. Essentially, "[while] there is no simple relationship between nitrogen and how much algae are growing in the water...there is a relationship: the greater the amount of nitrogen in reach, the greater the probability of finding high densities of algae." Consequently, since nutrients (including nitrogen) are typically in abundant supply in wastewater ponds, the next limiting factor in algae growth is usually the supply of dissolved oxygen.
In aerated lagoons and treatment plants, an overgrowth of algae will increase measured total suspended solids (TSS) and biochemical oxygen demand (BOD). If these measurements exceed permit levels, fines can add up quickly. As if those weren't enough problems, algae also create surface scum, cloudy water, noxious odors, and it can clog filters or damage equipment.
An exceedingly simple but effective method to prevent the growth of algae is to simply deprive it of sunlight using a device sometimes called a launder cover. These covers work on the principle that while beneficial bacteria do not require sunlight to perform their duties, algae cannot survive without photosynthesizing. Covering wastewater ponds with a material that effectively blocks sunlight will not only kill existing algae but will prevent it from ever gaining a foothold. Lagoon covers are a relatively simple answer to some severe and complex problems.
Wildlife
Open bodies of water, whether in a pond or an above-ground containment system, inevitably appeal to wildlife, birds, and the occasional wandering human. Some stroll by for a quick drink in the dead of night; others shelter from bad weather. No matter the means, exposure to wastewater can lead to illness and death.
Acids, cyanide, oil, and salts can kill simply through contact. In Alberta, Syncrude has paid multiple fines after repeated incidents where thousands of ducks and other aquatic birds have landed on their wastewater ponds. Most birds, covered with oil or having ingested toxic byproducts from tar sands mining, are found dead or so severely injured that they must be euthanized. This problem continues despite the employment of deterrents that include flashing lights, loud horns, and nets. Many companies, including Syncrude, continue to endure financial and social fallout.
One traditional method of discouraging wildlife is to cover wastewater ponds, lagoons, and holding tanks with nets. These can effectively prevent birds from landing, but it doesn't remove the attraction for other wildlife. Netting on in-ground impoundments doesn't control the growth of weeds in or around the pond, which also encourages wildlife to approach.
Pets and humans are vulnerable to open wastewater ponds as well. Dogs, in particular, are not discouraged by unpleasant smells and will willingly drink from ponds rife with bacteria, viruses, and toxins. Humans are slightly more discerning, but curious children are often willing to wade into or dip their hands in wastewater.
Covered wastewater ponds eliminate this issue. A covered lagoon does not appear to be a body of water, so it doesn't attract wildfowl. Deer, dogs, and other creatures are less likely to approach, and in the case of floating covers, children are unable to wade in. Issues with ecological damage and, even worse, personal injury can be tragic and are nearly always inflammatory. The benefits and practical insurance of covered wastewater impoundments offer high, long-term value compared to installation and maintenance costs.
Chemical consumption
Wastewater treatment calls for the use of chemicals such as chlorine and other disinfectants, which are expensive and potentially hazardous to employees. Open wastewater ponds are vulnerable to dilution due to excessive rainfall, while UV exposure can cause degradation of the chemicals. Extreme temperatures, especially on the upper end of the scale, can render disinfecting treatments worthless. Volatile, chemical disinfectants in uncovered storage rapidly lose potency as they evaporate or degrade. Wastewater covers minimize or eliminate this problem. Customized designs and features to address the needs of a particular installation may increase the initial cost of wastewater covers. Still, increased efficiency, safety, and cost savings for the entire operation can quickly recover the initial investment.
Odors and Gas
Okay, maybe it's not this bad, but plant operators frequently dismiss concerns about wastewater odors as unsolvable. Be that as it may, neighbors in the vicinity don't want to smell methane and other gases released during treatment. Virtually any kind of odor will raise complaints, and residents can become quite vocal about their unhappiness. These are more than an unpleasant nuisance — property values may become depressed, and public ill-will arising from noxious smells can interfere with approvals for facility expansions and improvements. Local resistance to the stench from a poorly managed wastewater operation may even block new programs for beneficial reuse of the treated water.
Sewage, wood pulp, animal waste (both manure and slaughter), and food processing waste, produce odors ranging from unpleasant to unbearable and may accompany hazardous contaminants. Mining operations, petrochemical plants, and many manufacturing plants generate waste with offensive and potentially dangerous emissions. Ammonia emissions from organic wastewater processing, for example, represent significant respiratory hazards for workers and can cause skin and eye irritation and pneumonia with extended exposure.
A balanced mix of bacteria in both aerobic and anaerobic lagoons makes little to no noticeable odor, even at close range. Anaerobic lagoons often bear the brunt of the blame for any detectable funk regardless.
Fortunately, floating covers can fully control offensive and hazardous odors produced during wastewater processing. Solid floating covers that sit directly on the water's surface eliminate contact with air, significantly reducing odors. Others work by sealing the cover to the wastewater basin and installing systems to divert and collect gases produced by digestive processes. Methane and other collected gas can be directly employed to provide heat, power machinery, or generate electricity on-site. Lagoon covers used for agricultural gas collection can present a low-maintenance, cost-effective solution to:
- Prevent floods and dam collapse caused by extreme rainfall events
- Maintain ideal temperatures for biological digestion
- Control odors in surrounding communities
- Bar wildlife access
- Produce fertilizer in a form ideal for crops.
