Characterization of Industrial Dairy Wastewater and Contribution to Reuse in Cereals Culture: Study of Phytotoxic Effect

Research Article

Austin J Environ Toxicol. 2016; 2(2): 1013.

Characterization of Industrial Dairy Wastewater and Contribution to Reuse in Cereals Culture: Study of Phytotoxic Effect

Sioud O, Beltifa A, Ayeb N and Mansour HB*

Analysis and Research Unit Processes Applied to the Environment-Higher Institute of Applied Science and Technology, University of Monastir Mahdia, Tunisia

*Corresponding author: Hedi Ben Mansour, Analysis and Research Unit Processes Applied to the Environment-Higher Institute of Applied Science and Technology, University of Monastir Mahdia, Tunisia

Received: June 08, 2016; Accepted: August 22, 2016; Published: August 30, 2016


The present work aims to study the impact of dairy effluents on seed germination and seedling growth of Wheat (Triticumaestivum) and Maize (Zea mays). Dairy effluents were collected from the inlet and outlet of waste water treatment plant of two dairy industries located in Tunisia in the areas of Sousse and Mahdia. Different physical and chemical parameters were evaluated for the assessment of effluents quality before and after treatment. Total suspended solids, BOD5, COD, detergents and Oils and fats of both Mahdia and Sousse dairy effluents decreased after treatment and were within permissible limits. While in the case of total Kjeldahl Nitrogen and total phosphorus, the reduction remained above limits. The use of treated effluent from both dairy plants enhanced seed germination and seedling growth of wheat. However, results showed inhibitory effect from the same effluents on maize seed germination and growth of roots and shoots. Observation showed that untreated effluent from Sousse dairy plant had inhibited seed germination for both wheat and maize but induced seedling growth.

Keywords: Dairy wastewater; Wastewater valorization; Phytotoxicity; Germination


Water resources in the Mediterranean are limited and very poorly distributed in space and in time. However, the demand for water has increased during the second half of the 20th century. Industrial activities (such as textiles, chemicals, food...) consume a high quantity of water and generate wastewater that increases the risk of water shortage and pollution of water resources, surface water and groundwater. Among all of these industries, dairy industry is strategically located in the Tunisian food industry and affects the country’s food security as it is an important economic niche (livestock, collection, processing, self-sufficiency...). However, this branch is characterized by a high consumption of water and generates, therefore, large quantities of wastewater discharge and sludge fat. This dreadful load is a source of environmental pollution, and an economic burden in relation to the treatment processes employed by producers.

Due to the increase in demand, water management involves the application of techniques that increase natural water supply, such as reused water. In recent years, the reuse of wastewater has been considerably developed. The current daily volume of used water reaches a staggering 1.5-1.7 million m3 per day in several countries, such as the U.S (California and Florida), Mexico and China [1]. The treated wastewater can be considered a «new» water resource that can be added to the overall assessment of water resources of a region. Bixio and al (2005) have classified different types of reuse into 4 categories (i) agricultural use, (ii) urban and peri-urban use and replenishing the aquifer (iii) industrial use and (iv) mixed uses [2].

In fact, agriculture consumes over 70% of water resources in developing countries such as the Arab countries (REJEB SALOUA, 2011). Indeed, the delivery of treated water to agricultural fields would decrease the negative impact caused by the use of clean water in irrigation [2]. In addition, the treated wastewater can balance the natural cycle of water and conserve resources by reducing harmful emissions into the environment [3]. Treated wastewater can sometimes be a superior source for agriculture than some fresh water sources. Nitrogen (N) and Phosphorus (P) in the wastewater may result in higher yields than freshwater irrigation, without additional fertilizer application [4].

According to the international standards, Tunisia is a country poor in water. With a level of renewable resources per capita per year not exceeding 450 m3/capita/year, water is a barrier to social and economic development in the country. Tunisia is characterized by an arid climate and scarce water resources (an annual average of 4.8 m3 of surface water and groundwater). Much of this water is salt water since 28% of surface waters have salinity greater than 1.5 g/l and 47% of the groundwater has salinity than 3 g/l (REJEB SALOUA, 2011). To cope with this water deficit the use of wastewater for irrigation has become a necessary solution and an integral part of the country’s water management strategy. According to these observations, we opted in this work to study a possibility of agricultural reuse of the untreated or treated wastewater collected from two dairy industries in Tunisia for irrigation. We started our work analysing the quality of water at the inlet and outlet of wastewater treatment plant of Mahdia and Sousse. Then we studied the effect of dairy effluents on the wheat and maize germination and growth.

Experimental Protocols

Wastewater samples

Wastewater samples were collected from the inlet and outlet of wastewater treatment plants of two dairy industries located in Mahdia and Sousse: Sousse Dairy Plant “SDP” and Mahdia Dairy Plant “MDP” in February, March and April 2015.

Physico-chemical analysis of wastewater samples

The samples were analysed for various physico-chemical characteristics. Turbidity and conductivity were determined using AQUALITIC® (Dortmund, Germany), Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) were determined according to the method of Hur, et al (2010).

Seedling growth

Wheat (T. aestivum L.) and maize (Zea mays L.) seeds were provided by the National Institute of Agronomical Research (INRA), Tunisia.

Seeds were raised in a soil mix of 2/3 sand and 1/3 compost. Thirty seeds were sown in each batch at 25±°C. The seeds were irrigated with treated and untreated wastewater from each dairy plant considered in this study. Controls were irrigated with distilled water. A number of seed germination was counted after six days of incubation.

Germination percentage: The germination percentage is the proportion of germinated seeds in relation to the total number of viable seeds that were tested by following formula:

%G=(Number of germinated seeds/Total number of planted seeds)×100.

Determination of elongation: The elongations of roots and leaves were measured with a ruler. Calculations were performed based on leaf lengths and major axial root averages.

Length Vigour Indices (VI): The length VI of seedling was calculated as below.

The length VI=(Mean Root Length + Mean Shoot Length). Percentage Germination [5].

Seedling Tolerance Index (TI): The tolerance index of seedlings was calculated by the formula:

TI = Mean length of longest root in treatment/Mean length of longest root in control [6].

Relative Toxicity (%RT): The relative toxicity (%RT) of each industrial wastewater, before and after treatment on the seedling growth, was calculated to determine the degree of inhibition over the control using the following formula:

%RT=(X-Y)/X×100 [7].

Where X refers to the seedling length in the control after six days of incubation and Y is the seedling length in the presence of each industrial effluent (before or after treatment) after six days of incubation.


Physicochemical analysis of dairy wastewaters

The physicochemical parameters of effluent samples were given in (Table 1). In general the physicochemical parameters of the treated effluents samples from the output station of both dairy industries fall within permissible limits set by Tunisian norms for release into the public domain (TN.106.002) except for some parameters. Total Kjeldahl Azote and total phosphorus values of untreated wastewater for both SDP and MDP exceeded the permissible values. High levels of suspended solids (4100 mg/L), total Phosphorus (47.5 mgP/L), detergents (2.76 mgABS/L) and Oils and fats (600 mg/L) were recorded in untreated wastewater from MDP. Important values of BOD5, COD and Total Kjeldahl Nitrogen, which are considered as pollution indicators, were also recorded for untreated wastewater from MDP. These parameters were higher compared to those of untreated wastewater from SDP.