**1. Introduction**

The tomato industry is among the most polluting food industries in its huge amount of water consumption. This wastewater is predominantly loaded with organic wastes and is rich in organic content (Bozinis et al., 1996). Biological treatment processes are widely used for the treatment of agro-industry wastewaters, such as tomato industry wastewater which contain high concentrations of biodegradable organic matter (BOM) (Satyanarayan et al., 2005; Tawfik & El-Kamah 2011). Anaerobic treatment of high strength wastewater is widely accepted in the industry (Tawfik et al., 2008; Mehrdad et al., 2007; Del Pozo et al., 2003; Bernet &Paul, 2006). It has several advantages over aerobic processes, which include the use of less energy due to omission of aeration, the conversion of organic matter to methane which is an energy source by itself and can be used to supply some of the energy requirement of the process. Lower production of sludge, which reduces sludge disposal costs greatly and low level of maintenance, are other benefits of anaerobic processes (Tawfik et al., 2006; Cakira & Stenstromb, 2005; Shin et al., 2005). Moreover, high substrate removal efficiencies would be achieved in anaerobic reactors with short hydraulic retention time (HRT) and high organic loading rate (OLR) (Tawfik et al., 2010). One of the most efficient and quite flexible designs available is an anaerobic hybrid (AH) reactor which combines advantages of both anaerobic filter (AF) and up-flow anaerobic sludge blanket (UASB) designs (Chang ,1989; Hawkes et al., 1995; Wu et al., 2000; Tawfik et al., 2011; Mahmoud et al., 2009). The presence of polyurethane media in the upper portion of AH reactor, in addition to its physical role for biomass retention, also exerts some biological activity which contributes to chemical oxygen demand (COD) reduction in a zone where generally active biomass is lacking in a calssical UASB reactor (Elmitwalli et al., 1999; Tawfik et al., 2009). However; the effluent quality of anaerobic reactor is still not complying in terms of COD,

total suspended solids (TSS) and nitrogen for discharge into drainage canals. Therefore, post-treatment is needed. Trickling filter (TF) is one of the aerobic biological treatment systems that are widely used for post-treatment of anaerobically pretreated effluent. However, the TF still has some drawbacks such as difficulty in maintenance of appropriate biofilm thickness under limitation of oxygen supply and biofilm detachment from the packing materials. In this investigation polyurethane trickling filter (PTF) was proposed. It has several advantages compared to conventional TF. In TF of which micro-organisms attach themselves only to a media surface creating a biological filter or slime layer, but in PTF module, the micro-organisms are retained outside and inside the polyurethane media which create long sludge residence time (SRT>100 days) (Tawfik et al., 2006) and consequently, achieve a complete nitrification and produce a very low amount of sludge (Tawfik et al., 2006). Once again, PTF brings the following advantages compared to conventional TF, the amount of active biomass brought in contact with the wastewater is very high and the biological process is very fast, thus very short retention time is needed which gives small plants with no investment cost (Tawfik et al., 2010). The process is in contrast to conventional TF which needs a very low OLR to achieve a nitrification process (Tawfik et al.,2011; Chernicharo &Nascimento, 2001). Moreover, it is easy to enlarge the capacity of PTF system in case the flow and/or the organic load would increase in the future.

Polyurethane Trickling Filter in Combination with

Anaerobic Hybrid Reactor for Treatment of Tomato Industry Wastewater 357

0.57m2. NaHCO3 was added to adjust the influent pH in the range of 6–7. The seed sludge was taken from an up-flow anaerobic sludge blanket (UASB) reactor treating juice industry wastewater. The sludge is typically flocculent with mixed liquor suspended solids (MLSS) of 16.8 g/l, mixed liquor volatile suspended solids (MLVSS) of 10.8 g/l and VSS/TSS ratio of

0.64. Three liters of the sludge was pumped into the AH reactor as an inoculum.

**Figure 1.** PTF module coupled with AH reactor for treatment of tomato industry wastewater

The PTF is packed with porous polyurethane foam (pore size= 0.63 mm) with relatively high specific surface area (256 m2/m3) to increase both the biofilm mass content and the removal efficiency of the reactor. The PTF module used in this study, consisted of three segments connected vertically in series. The polyurethane represents 15% of the total reactor volume (23l) (Fig. 1). Polyurethane media was warped with perforated polypropylene material (0.5 cm) to avoid clogging of the media and facilitate the air penetration inside the packing material. The PTF was equipped with 276 pieces each 40 mm height and 20 mm in diameter with 90% of porosity. The reactor was operated without inoculums. The distributer is situated on the top of the reactor and operated at 18 rpm for equal distribution of wastewater over the packing material. The air was naturally diffused to the reactor via three windows along the reactor height. There is no need for aeration as well as no backwashing.

**2.3. Polyurethane trickling filter (PTF) reactor** 

The objectives of this investigation are to 1. assess the efficiency of a combined system consisting of AH reactor and PTF for the treatment of tomato industry wastewater at different HRTs and OLRs with emphasis on the COD fractions (CODtotal; CODsoluble and CODparticulate); TSS and total nitrogen (TN) removal. In addition, the mechanism for the removal COD, TSS and nitrification efficiency along the height of PTF is investigated.
