90
used to store the wastewater to be treated, and the water is circulated through the pipes by a
1/2 HP pump. The pipes exposed have a 12 L volume approximately.
Horizontal Sub Surface Flow (HSSF) constructed wetlands consisted of four concrete
containers that were arranged in a parallel configuration. The containers were located near a
wastewater treatment plant that provided service for the university population. Each of the
wetland treatment units measured 1.0×0.6×0.6 m deep and was backfilled with local gravel
substrate (average dimensions of 8 to 10 mm). Wetland bed was planted with 25 seedlings-
rhizomes of
Cyperus ligularis
. The wetland was planted in July 2013 and was subsequently
monitored.
Operation and wastewater quality monitoring.
Storage tank is filled up with 40L of
wastewater previously clarified in a settling tank and then the water is circulated through
the pipes: the water is pumped from the storage tank through these and is discharged in the
same tank, ensuring batch operation mode. Hydrogen peroxide was added in the tank at the
beginning of the tests. The residence time was 5 hours, at times when UV indices were
higher (about noon).
Untreated water (influent) and treated water (effluent) were taken before and after 5 hours
of residence and analyzed for COD, ammonia–N, Hydrogen Potencial (pH),
oxidation/reduction potential (ORP), dissolved oxygen (DO), electric conductivity,
turbidity, temperature and fecals and totals coliforms. Measurements and analyses of water
samples were as described in APHA-AWWA-WEF (2005) or according to manufacturer’s
guidelines. Total and fecal coliform bacteria populations are enumerated using the
membrane filtration method using 0.45 μm pore size membrane filters (Millipore Corp) and
selective agar EMB (Eosin-Methylen blue). Measurements of
In situ
parameters are
obtained using a WTW Multiparameter (Multi 9430).
Four photolysis tests were carried out, where the wastewater was exposed to sunlight
without any addition of an oxidizing agent. Then, tests were executed using three doses of
hydrogen peroxide (4 tests per dose): High (300 ppm), Medium (30 ppm) and Low (3
ppm), in order to find an optimal dose for the degradation of COD, ammonia -N and total
and fecal coliforms. When the coupled system is evaluated, the effluent from the wetland
will be treated in the photoreactor using the optimal found peroxide dose.
Results and discussion
Solar photoreactor Treatment.
Table 1 provides parameter values as a function of
treatment. Temperature increased after treatment approximately 10°C. Dissolved oxygen
concentration is proportional to peroxide´s dose. ORP changed from negative to positive
values indicating a shift from anaerobic to aerobic conditions, a fact which is justified by
the increased oxygen dissolved. Parameters such as pH, electrical conductivity and
turbidity showed insignificant variations.
Table 1. Averages (SD in brackets) of the water quality parameter in the influent and
effluents
Parameter
Influent
Photolysis
Low
Medium
High
