Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

CULTIVATION OF PHRAGMITES AUSTRALIS IN A CONSTRUCTED WETLAND FOR THE TREATMENT OF WASTEWATERS OF AGRICULTURAL ORIGIN

MARMIROLI N.*, MARMIROLI M.*, MAESTRI E.*, TAGLIAVINI S.*, MANTOVI P.**, PICCININI S.*

* Dip. Scienze Ambientali, Università di Parma, Parma

marmirol@unipr.it

** Centro Ricerche Produzioni Animali (CRPA) Reggio Emilia

Phragmites australis, phytoremediation, heavy metals, dairy parlour wastewaters

Several species of plants are increasingly utilised in different situations, not only for food and fodder production, but also for environmental protection, as is the case for phytoremediation. In this application, agricultural and agronomic practices are employed in the choice, cultivation and management of higher plants for the purpose of decontaminating polluted substrates, such as soils, sediments and water.

The application of phytoremediation techniques in the treatment of polluted waters (rhizofiltration or rhizosphere bioremediation) seems particularly promising in all those situations in which isolated settlements have difficulties in connecting or in utilizing conventional water treatment plants (large scale depuration). This is the case, for instance, of agro-industrial plants like milk and cheese production farms.

A constructed wetland consisting in two horizontal sub-surface flow beds to treat dairy parlour wastewaters and domestic sewage was built in 1999 in a mountain agricultural settlement, at 600 m above sea level, in Northern Italy. The plant was originally designed to treat wastewaters, which are more polluted than domestic sewage, from a dairy farm with an 80-cow herd: 3000 mg/l COD, with a 40% BOD, for a total of 25 liters wastewater produced by each animal each day.

Each bed was 12.5 m long by 6 m wide and 1.1 m deep with a base slope of 1.5%. They were lined with PVC and filled with gravel each to a depth of 0.9 m. Each bed was equipped with three vertical perforated tubes to control and sample water flow, at different positions of the bed’s length. The beds were planted with Phragmites australis in April 2000 on a total surface of 150 m². Pre-treatment of wastewaters was done in a septic tank followed by a plastic filter, both mainly used to store up suspended solids before they reach the reed beds.

Wastewater inflows and outflows were sampled throughout the first year of the trial, from April 2000 to March 2001. Analyses were done for pH, Total Suspended Solids (TSS), COD, BOD₅, total nitrogen (TKN), NH₄-N, NO₃-N, P and heavy metals (copper and zinc). Measured mean flow rates were 6m³/day.

The Phragmites reeds were sampled at the end of the vegetative period (October 2001) to determine above- and below-ground growth, chlorophyll and heavy metal content and to verify the occurrence of mycorrhizae in roots. Heavy metal distribution was also verified in plant tissues by means of Scanning Electron Microscopy and microanalysis (SEM/EDX).

The reed’s growth (root and shoot biomass, leaf number, plant height) in the first bed was significantly higher than in the second, whereas no difference could be evidenced in the frequency of occurrence of mycorrhizae. Significant differences could also be found for the zinc content in reed stems and roots. SEM/EDX analyses evidenced the precipitation of iron on the outside surface of the root periderm, reported to be acting as a barrier towards uptake of other metals.

The performance of the process was checked during the winter time to ascertain the feasibility of the treatment during the period in which plant activities are reduced.

The main results obtained from the whole system are shown in the following table. Bacteria transform input nitrogen in NH₄-N, then a nitrification process occurs in the presence of oxygen thanks to other bacteria strains. Probably the concentration in NH₄-N of the output water slightly increases because there is a general lack of oxygen that slows the nitrification reactions.

Parameter	INPUT	OUTPUT	Parameter	INPUT	OUTPUT
TSS (mg/l)	760	70	NH4-N (mg/l)	21,8	23,3
COD (mgO2/l)	1380	105	NO3-N (mg/l)	8,5	5,6
BOD5 (mgO2/l)	505	32	P (mg/l)	14,0	5,0
TKN (mg/l)	57,3	30,5	Organic N (mg/l)	35,5	7,2

According to the Italian legislation, wastewaters from dairy parlour are included in the regional law: “Legge della Regione Emilia Romagna 29 Gennaio 1983, n.7” and must conform to specific parameter values in order to be delivered to surface waters.

All parameters in the final outflow were therefore well below the acceptable values for discharge into water courses during the whole year of operation, showing that reed beds are able to reduce pollutant levels of wastewaters.