Odors
Odor concerns are raised at two key points: during the treatment process and in the storage and application of biosolids. Many of the odors associated with biosolids are reduced during the treatment process. As organic materials breakdown, odors are released. Thus is the case with biosolids, which like other manures will release odors. The method of biosolids treatment also affects odors. Lime stabilized biosolids will have a slightly sweet ammonia odor. Digested biosolids will have a more organic aroma. In most cases, odors dissipate after several days, similar to animal manures. The greatest odor release occurs after the biosolids are tilled into the soil. Generally, after proper tillage, the odors cannot be detected from the field within a couple of days of application.In the Perth metropolitan area buffer zones are used around the treatment plants to reduce the impact of odor on community residence. An odor impact study has recently been completed for the proposed biosolid storage facility in Moora. This study found that odor would not be detected beyond 1500m from the storage facility, and consequently would not impact on residence of the area.
Flies
An increase in the breeding and presence of flies has been reported during the storage and application of biosolids. The extensive transporting and temporary stockpiling of biosolids has the potential to facilitate the transportation of different fly species between areas and contribute to an overall increase in fly population.
Several research studies have been conducted into the relationship between biosolids and flies and the final conclusions are that biosolids do not support fly breeding if the solids content is greater than 40%, stockpiling of biosolids is conducted during the cooler months (May to October), the biosolids stockpile is covered to restrict fly emergence or the biosolids stockpile period is minimal (estimated to be less than 10 days) whereby potential fly emergence is considered to be very low. The Water Corporation is investigating methods to control fly strikes and is preparing a management plan to deal with this issue.
Pathogens
A major public health and environmental concern associated with land application of biosolids is the effect of pathogens on humans and animals. Pathogens are microorganisms that cause disease. Wastewater generally contains four major types of human pathogenic (disease-causing) organisms: bacteria, viruses, protozoa and helminthes (parasitic worms). Pathogens in general do not survive out of the body. Germs are vulnerable and will die when exposed to environmental conditions such as heat, sunlight, and desiccation. Approximately 99% of pathogens are destroyed during the treatment of wastewater, and most of the remainder through the biosolid treatment process – leaving the biosolids with similar bacteria levels to manure.
Storm water runoff
Biosolids absorbed to soil particles may runoff from land-applied fields into nearby streams and surface waters. In order to prevent water pollution, site restrictions are required. These include maintaining buffers along waterways and surface waters and restricting slopes where biosolids can be applied.
Groundwater contamination
Research over the past 30 years has found that biosolids posses little risk to ground water quality. In fact biosolids present a much lesser threat to groundwater than animal manure or commercial fertiliser, because, unlike manure and commercial fertilisers, biosolids are strictly regulated and applied to land at rates that meet the nutrient requirements of the crop.
Toxic Chemicals & Heavy Metals
In Perth, biosolids are relatively clean and free of heavy metals because of our low level of industry and strict industrial waste controls. Certain toxic chemicals that do not volatilize or decompose during treatment may concentrate in biosolids. Residues from the chemicals have declined significantly over the past 20 years. Biosolids are tested regularly for toxic chemicals. The Water Corporation (WA) provides annual data on the typical nutrient and contaminant concentrations in biosolids produced in our facilities. 06/07 data is currently available, and demonstrates that all levels are well within the national regulation guidelines.
Truck traffic
Biosolids are delivered to the site in tractor-trailers for cake biosolids. Concern has been raised about spillage and odour. In WA, these issues are managed through the use of enclosed trucks.