Integrated Use of Constructed Wetlands for Livestock Wastewater Treatment and Fodder Production

Constructed wetlands (CW) are widely used to treat wastewater (WW) because of its high efficiency for removal of pollutants, and low operational and maintenance costs. Plants play an important role in enhancing the WW treatment process in CW. Therefore, selection of the appropriate plant species to be grown in CW is an important criterion to ensure the success of the CW system. The performances of 5 plant species, namely, Typha (Typha spp), Dwarf Napier (Pennisetum purpureum), Guinea grass (Panicum maximum) and 2 varieties of Kenaf (Hibiscus cannabinus L) i.e. K 465/118 (K465) and Thai Kenaf grown in cattle WW were evaluated over 4 weeks. The different plant species were ranked using Typha (a widely use plant for phytoremediation) as a control based on their percentage of mortality, rate of growth of the root system, crude protein (CP) content, dry matter yield (DMY), and palatability score. The results showed that Typha had the highest score followed by Napier, K465 Kenaf, Thai Kenaf and Guinea. Based on the results of this study three plant species (Typha, Napier and K465 Kenaf) were selected for further evaluations in experiment 2. In the second experiment, the 3 plant species were grown in 3 different concentrations of cattle WW; low (COD 2,000 mg/L), medium (COD 7,000 mg/L) and high (COD 14, 000 mg/L) in a 3 x 3 factorial experiment arranged in a RCBD design. Almost all of the Napier plants died by the end of the 2 weeks adaptation period. Typha and Kenaf had the highest above-surface fraction (stems and leaves) fresh yield (FY) and DMY in the medium WW concentration. The nutrient content of the 2 plants increased with increased WW concentration. The under-surface fraction (roots) FY and DMY of Typha was positively associated with the WW concentration, while negative relationships were obtained for Kenaf. Pollutants removal by Typha from WW was more efficient than Kenaf. The third experiment was conducted to examine the efficiency of pollutants removal from cattle WW. It consisted of a 3 hydraulic retention times (HRT) (5, 10 and 15 days) x 3 plant types [Typha, Kenaf and no plant (as control)] factorial experiment, arranged in a randomized complete block design (RCBD) with 3 replications. On average, the removal efficiency ranged from 58 to 65 % for Chemical Oxygen Demand (COD) for the various treatments, 77 to 94 % for Total Suspended Solids (TSS), 60 to 79 % for Ammonium Nitrogen (NH+4-N), 51 to 65% for Total Kjeldahl Nitrogen (TKN), 50 to 60% for Dissolved phosphate (DP) and 50 to 61% for Total Orthophosphate (OP). Nitrogen and P removal efficiencies of the cells with plants were 11-19 and 7-11%, respectively, higher than unplanted cells; however, plants were not effective in COD and TSS removals. HRT contributed on removal efficiency for TSS and COD but not in nutrients removal. Effluent TSS for the 15 days HRT (46.7 mg/L) is within the permissible limit for effluent discharge from livestock WW in Malaysia. However, the average COD of the effluent discharge (684 mg/L) from different treatments was marginally higher than the permissible limit (500 COD mg/L) for effluent discharge from livestock WW in Malaysia. Typha and Kenaf plants grew well in the CW and exhibited their potential as phytoremediation agents and possibly as a source of animal feed.

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