2. Material and methods
2.1. Description of the systems
The goal and scope of the study was to analyze the commonly
available on-site wastewater treatment options for rural areas of
Finland. Six alternatives were chosen for comparison: 1) sequencing
batch reactor (SBR), 2) biofilter, 3) soil infiltration, 4) buried sand
filter, 5) holding tank for black water and soil infiltration for gray
water, and 6) dry toilet with gray-water treatment. Two subalternatives
were used for dry-toilets: soil infiltration A) or prefabricated
gray-water filter B). In the last two systems listed, gray
and black water were sewered separately. The alternatives chosen
represent average products on the market, not any particular
commercial products. All products are capable of reaching the
purification performance of the on-site decree (85% reduction in
phosphorous, 40% in nitrogen and 90% of biological oxygen demand
(BOD)).
The alternative on-site systems and the sludge treatment are
described briefly below, and a summary of the assumptions is given
in Table 1.
2.1.1. Sequencing batch reactor
A sequencing batch reactor is a prefabricated biologicale
chemical wastewater treatment plant in which the wastewater is
purified in batches. Its operation is based on an activated sludge
process. In addition, the phosphorus is chemically precipitated. The
SBR studied includes a polyethylene tank with two chambers
(storage and process), along with technical equipment, including,
for example, a central processing unit, four pumps (feed, discharge,
sludge, and chemical), an air compressor, and internal pipework.